Posted by Elaine Becker on Fri, Apr 20, 2012
Much of this blog series has been focused on the instrument and getting the best possible inter-instrument agreement. However, we can’t forget the basics of good practice in color measurement when it comes to sample presentation. Some types of samples can be very repeatable to present to the instrument, while others pose more challenges.
Sample presentation can contribute a significant amount of error to the total “error budget” in a color measurement system. A gauge R & R test should be performed to assess the amount of variance contributed by your current measurement procedures. To improve on this number, follow this list of basic principles to minimize the error contributed to a sample measurement from sample presentation.
- Sampling – Take a sample that is representative of the product by making sure that the batch or lot you prepare for testing is homogenous and mixed completely.
- Conditioning – Prepare the samples in the same way each time paying attention to heat and humidity. Samples should be allowed to equilibrate to room temperature before measurement
- Follow basic rules for good sample presentation
- Be consistent
- Clean
- Free of dirt, grease, and fingerprints
- Flat area
- Free of scratches and imperfections
- If possible, mark the area that was measured on the back of the sample so that it can be duplicated if needed
Depending on the application, there can be certain things to note or to watch out for:
Paint & Coatings – While these are usually nice, smooth, and easy samples to measure, the operator needs to be sure that the sample he is measuring is opaque. If not, then the sample film thickness needs to be measured and noted because opacity will definitely affect the reading. If steel or metal panels are sprayed with the coating and then measured, make sure the sample is flat. If not, then apply sufficient pressure to the sample back during the measurement to make the sample flat and in complete contact with the sample port.
- Plastics – The same guidelines given for coatings also ap
ply to plastics. Opacity can be a particular concern as can sample bowing or lack of a planar surface. Whenever curved parts are measured, it is necessary to be very careful about the position on the sample being measured and the amount of pressure applied.
- Textiles – A typical problem with many textile samples is non-uniformity
- Use sample averaging
- Specify the procedure and areas to be measured and number of spots to be averaged
- Specify how many sample thicknesses are to be measured.
- Be aware of “pillowing” – this happens with soft and pliable samples when too much pressure is applied and the sample can actually protrude or “pillow” into the measuring port.
- Many textile samples exhibit directionality. Be consistent about the direction of the grain or texture and which way to orient the sample or else use a procedure that rotates the sample 90 after each reading (and be sure to include all 4 orientations in the average).
- Textured samples will require the use of sample averaging to minimize the affects of texture on the sample
- Ink and printed samples can exhibit some of the issues described above such as opacity, non-uniformity, and directionality. Film thickness can be inconsistent within a print or strike-off and therefore sample averaging is usually necessary.
Food samples invariably require a customized procedure for consistent and repeatable measurement. Use of clear containers, cuvettes, and Petri dishes will help to provide for stable, consistent reading in food applications. Sampling can be very important too in making sure that the sample being read really represents the color of the whole batch.
-
Liquids and chemicals exhibit many of the same challenges as f
ood samples. Finding the proper sample container can resolve many of the problems. With odd shaped items, a sample jig will most likely be needed for consistent placement.
Assessing the variability in your sample presentation can point out areas where you can improve your procedures and thereby increase the precision of your color assessments, and facilitate the exchange of reliable electronic color data.
Posted by Elaine Becker on Wed, Feb 22, 2012
One of the latest advancements in color technology is instrument profiling. Instrument profiling is used to make a population of spectrophotometers read to within a tighter specification of each other thereby improving Inter-Instrument Agreement. A master instrument is used as the reference point and all other instruments are “cloned” to match this master instrument. A complex set of equations is used to profile or “correct” a target instrument so that its spectral data mimics that of the master. After profiling, all data taken on the target instrument is now corrected to match the master. The result is much tighter agreement between instruments which leads to fewer disputes over whether the color match is acceptable and faster acceptance and approval of submits.
Why do I need to profile my spectrophotometer?
In order for electronic standards to “work” within your supply chain, you need to be able to recall a stored standard, measure the actual stored standard on another instrument and have a resulting DE of 0.15 or less. The number of 0.15 is dependent on how tight your tolerances are. If you are trying to supply a color match that is <0.5DE, then you certainly don’t want to have half of that deviation taken up by lack of inter-instrument agreement. A good rule of thumb is that no more than 25% of your tolerance should be given up to instrument variables (such as INTER-INSTRUMENT AGREEMENT, sample repeatability, and instrument repeatability). So if your tolerance is DE=1.0, then you can live with measurement uncertainty of up to 0.25DE. If your tolerance is DE<0.5, then you can live with an uncertainty of no more than 0.125. So as tolerances get tighter and customers get more critical of color, INTER-INSTRUMENT AGREEMENT becomes more important. Instrument profiling can help you achieve the INTER-INSTRUMENT AGREEMENT that you need in order to meet these tight tolerances.
- How do I do this?
- What’s needed to begin profiling the instruments in mycolor network or supply chain?
- How often do I need to profile?
- What benefits will I receive for my efforts?
You can get answers to these questions, learn more about instrument profiling and download a white paper on the subject by clicking the button below.
Posted by Elaine Becker on Mon, Oct 31, 2011
What is Inter-Instrument Agreement? Should I care? How do you determine it? How do I know what my numbers are? Can I measure it myself?
Inter-instrument agreement is a measure of how closely two or more color instruments read color the same. In layman’s terms it measures how close your absolute L*a*b* readings are to someone else’s on the exact, same samples.
Why should I care about inter-instrument agreement? The most important reason is to be able to share electronic color standards and colorant databases. If you are trying to compare the color values taken on your spectrophotometer to those taken on another spectro, conventional wisdom has long held that you could compare the deltas or color differences on a set of samples, but not the absolute values. However, in today’s workplace technology has made it extremely easy to communicate absolute as well as color difference values. Many companies are successfully sharing electronic color standards not only within a company but within a supply chain around the world.
How do you determine the inter-instrument agreement? 
Typically inter-instrument is a test done by the instrument manufacturer in the quality assurance process of manufacturing an instrument. The new instrument is compared to the “master” instrument or the average of a population of typical instruments. Usually a set of 12 BCRA tiles plus a white and black tile are used for the test. The tile set is measured on the target instrument and compared to the known values as measured on the master instrument. A color difference for each tile is calculated between the master and the target instrument. Then the DE’s are averaged over all the tiles and this number becomes the Inter-instrument agreement for the target instrument. Manufacturers of instruments publish their specification or limit for the DE between instruments. The average DE over these 14 tiles must be less than this number to “pass” their quality control testing. Each DE on an individual tile must also be less than a certain limit, although this limit is not always published.
What if I want to compare my spectrophotometer to my supplier’s or someone else’s instrument in the supply chain? Can I do this myself? Certainly you can. First you need to understand that when instrument manufacturers do this test, it is always in very controlled conditions for temperature and humidity. You will need a set of durable and stable color standards such as BCRA tiles or a Diagnostic Tile Set from Mount Baker Research. Ceramic tiles are the best transfer standards to use since they are the most stable and durable materials currently available.
The same set of ceramic tiles must be read on each instrument under controlled conditions of temperature and humidity. The instrument settings for specular component, UV component, and aperture size and lens setting must be the same for both instruments. The readings from the target instrument are then compared to those from the master instrument and a DE is computed between the two readings. Usually D6500, 10 ° observer, and CIE L*a*b* are used for the comparison. After obtaining a DE for each tile, the average DE for all the tiles is computed and this is the value typically used to specify Inter-Instrument Agreement.
What kind of numbers should I expect? What can I do to make it better?
You may be surprised to find out that your inter-instrument agreement numbers are larger than the published data from the manufacturer. First of all, when done by the manufacturer, the reference instrument is always an instrument that has been maintained in pristine condition and is designated for this purpose. When you do the test, you are comparing two production machines that may be as far apart as allowed. Therefore, if the specification on the IIA is DE*<0.15, then it’s possible for the two units under test to be as far as 0.30 apart and still be in spec. While that is not the normal case, the bigger difference can be attributed to the actual wear and tear and environmental conditions that the instrument is used under. No doubt all instruments will meet the manufacturer’s spec “right out of the box”. However in the “real world” of color measurement, instruments are used under less than pristine conditions, and dust and dirt can wreck havoc with the fine optics of a spectrophotometer.
What can you do to make it better?
A disciplined approach to monitoring instrument performance is crucial. The simple daily calibration routine is not enough to ensure that your spectro is performing within specification. While adding a daily green tile test to the routine is advisable, it is still not the complete answer to knowing whether your instrument is measuring color precisely.
There are two things can do to ensure that your instrument is working properly. Tip #5 in this series will tell you how to do this and Tip #6 will discuss how instrument profiling is used to give you the best possible Inter-Instrument-Agreement between spectrophotometers.
Posted by Elaine Becker on Wed, Jun 15, 2011
It all starts with the instrument you choose! The single most important element in communicating electronic color data is the spectrophotometer. You must use spectrophotometers; colorimeters ( by this I mean 3 filter tristimulus colorimeters) are not designed to be “absolute” instruments and are not suitable for sharing absolute color data, such as electronic color standards. They are designed to be “difference” meters. So using a spectrophotometer is essential to success!
When communicating electronic color data, you need to specify the make and model of the instrument. This defines the instrument geometry. Also, note that it’s not possible to mix sphere (d/8) geometry with 45/0 geometry. You can’t share absolute data between instruments that have different geometries. That means you can’t mix sphere geometry with 45/0 or 0/45 geometry. The instruments just read and handle the gloss of a color differently. One is not right and the other wrong; they are just different in the way they measure color and handle the specular reflectance or gloss.
While the higher end benchtop spectrophotometers provide the best precision and accuracy, many of today’s handheld or portable spectrophotometers are also well-suited to the task. Instruments from the same manufacturer tend to have better inter-instrument agreement than when mixing spectros from different manufacturers; and those within the same make and model from a manufacturer will yield the best inter-instrument agreement. So unless you are using instrument profiling, your best chance for getting instruments to agree on a color measurement is to stick with the same make and model. More on instrument profiling in Tip #4.
Instrumentation must be kept in tip-top condition. Your instrument should be monitored on a regular basis and standardized yearly. A daily green tile test is a good screening tool to verify that the instrument was calibrated properly and can catch any gross errors in the instrument performance. But the green tile test is not a guarantee that your instrument is reading all colors properly and can’t detect subtle changes in drift and aging. You should also do a monthly diagnostic test with an extended set of ceramic tiles. A future blog on Tip #5 in this series on “Monitoring Your Instrument Performance” will address this topic.
To summarize:
- Use a spectrophotometer, not a colorimeter
- You can’t mix sphere geometry with 45/0 or 0/45 geometry
- Use the same make and model of spectrophotometer
- Make sure the instruments are serviced annually
Posted by Elaine Becker on Thu, Apr 28, 2011
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Using electronic color standards and sharing L*a*b* color values is the goal of many companies and their supply chains these days. It’s easy, fast, and convenient. If we’re all using the same numbers for our color target, isn’t that the best way to assure that we’re all matching to the same color? It is certainly more convenient than shipping samples around overnight. But before you do so, you need to understand the best practices of color measurement and for setting and maintaining numerical color standards. Many color disputes arise these days because color instruments don’t necessarily read the same. Electronic or numerical color standards are widely used and shared within a supply chain and have many benefits, but if all of your instruments are not regularly monitored and calibrated, then problems can arise.
Electronic color standards are used widely in the coatings, plastics, textile, and printing industries. As Shelley Sturdevant, the North American Technical Director for Coil and Extrusion Coatings for PPG will tell you, the benefits are huge in terms of consistency of color, easy global color communication, and cost effectiveness if done properly. Color can be communicated instantly around the world and manufactured consistently to the same stored color standard. Electronic color standards are permanent and don’t change with use and over time. Read more of her comments in “Spot On: Lessons From a Color-Matching Master”. But what do you need to know and understand about the process in order to make it work for you? This blog lays out 10 key points that you need to pay attention to and sets the stage for the next 10 blogs which will delve into each item in more detail.
Future blogs will discuss each of these 10 aspects of using electronic color standards to help you avoid some of the pitfalls. Click on the links below for a more detailed discussion of each topic:
- Instrumentation – It all starts with the instrument!
- Measurement Conditions – What do you need to specify?
- Physical standards – Don’t I just grab a sample and measure it?
- Inter-instrument agreement - How do you determine it? What if I want to compare my spectrophotometer to my supplier’s or someone else’s instrument in the supply chain? Can I do this myself?
- Monitor Instrument Performance –Is the green tile test really enough?
- Instrument Profiling – or how to improve your inter-instrument agreement
- Sharing the data – How?
- Sample presentation – What are the variables?
- Translucency & Fluorescence – What types of physical samples just don’t work well with electronic standards?
- Do an audit – The ultimate test for “Is it really working?”
Does your company use electronic color standards? Within just your company or with your supply chain?
Posted by Elaine Becker on Wed, Jun 16, 2010
This blog post was authored by John W. Root of Mt. Baker Research.
Workers in digital imaging and publishing use color management to achieve consistency throughout a workflow. The goal is to preserve the quality and accuracy of an image from capture to final reproduction. Each device in the workflow supports a different color space. The available color management systems profile the gamut capabilities of each device, and then limit the working color space to the gamut that is shared by all of them.
The workflow used by color metrologists is different. Many labs employ more 
than one instrument to measure color or appearance and to assure quality control. Here we'll focus on measurements of spectral reflectance factors ("SRF") for uniformly colored samples. A spectrophotometer is used to measure SRF data throughout the visible spectrum, which extends from 400 - 700 nm.
Different instruments may not output the same SRF data based on measurements of the same transfer standard. In this situation tests of inter-instrument agreement may be used to measure the consistency between the participating instruments. Depending on the outcome of these tests, color management may be required to enable the meaningful sharing of SRF data.
Inter-instrument agreement cannot be achieved unless the test instruments employ the same geometry. See Color Geometry: A Matter of Degrees (another post within this blog) for a discussion of geometry.
In printing and the graphic arts metrologists who use sphere-based instruments employ the (d/8°) diffuse hemispherical specular-excluded ("SCE") geometry. Others prefer the (0°/45°) or (45°/0°) bi-directional geometry. Because gloss is important in the manufacture of paints and architectural ceramics, in those industries metrologists prefer the (t/8°) total hemispherical specular-included ("SCI") geometry, although certain segments of the coatings industry, namely coil coating, have standardized on 45°/0° geometry.
Among comparable instruments that use the same geometry, other factors may lead to differences in the measured SRF data. Before listing these factors, we stipulate that the instruments to be compared are maintained in good working order, and that suitable procedures are used to achieve consistent sample quality and to measure accurate SRF data.
Differences in the SRF values measured by comparable instruments may result from the following types of wavelength-dependent error: (1) Photometric scale. (2) Wavelength scale. (3) Bandwidth.
The standard multivariate regression procedure that is used to characterize these errors was described in the open literature more than 20 years ago. In a complementary approach, during 2009 the author developed transfer standards that are optimized for detecting these errors. For more information see Color Measurement Accuracy: Diagnostic Procedures (another post within this blog).
The multivariate regression procedure detects and measures the following errors: (1) Photometric zero (black point). (2) Photometric linear scale (100% reflectance line). (3) Photometric nonlinear scale. (4) Wavelength scale. (5) Bandwidth. This method cannot compensate for differences in instrument geometry, or for the errors that result from thermochromism or lateral diffusion. For a discussion of translucency see Color Measurement Accuracy: Translucent Materials (another post within this blog).
CyberChrome's OnColor Profiler® profiling system can analyze the errors listed above on most of the instruments that are in use today. This system includes software and 32 reduced-translucency transfer standards that are optimized for profiling. The OnColor Profiler® software compares the SRF data measured on each test instrument with data from a master instrument. The software generates correlation coefficients, or correction factors, that may be used to improve inter-instrument agreement with the master instrument. See How to improve Inter-instrument Agreement with Instrument Profiling (another post within this blog).
The author of this article is John W. Root Ph.D. of Mt. Baker Research who can be reached via email at jackroot@mtbakerresearch.com.
Posted by Elaine Becker on Thu, May 27, 2010
This blog post was authored by John W. Root of Mt. Baker Research.
During 2009 Mount Baker Research introduced transfer standards and procedures for 
diagnosing instrument errors. Parts A and B of the Diagnostic Tile Set each contain 16 2 x 2 inch ceramic color standards. Part A supports instrument testing and the assessment of inter-instrument agreement in a multi-instrument environment. Part B enables licensed users of part A and CyberChrome's OnColor Profiler® software to upgrade to profiling.
The part A standards were selected to meet the following criteria: (1) Span the complete photometric range. (2) Span the widest possible high-chroma gamut in CIELAB color space. (3) Include only high quality standards with minimal translucency.
List of Supported Tests
1. Instrument Validation. For this test the part A standards must be pre-calibrated in the geometries of interest. (Three geometries are supported.) After the user measures spectral reflectance factors ("SRF") with the test instrument, statistical data analysis is used to diagnose its performance and compare it to a reference instrument.
2. Absolute Accuracy. To characterize the absolute spectrophotometric accuracy, the SRF data from the validation test may be compared with data measured at NRC for similar transfer standards. At present this test is supported for the (0°/45°) and (45°/0°) geometries.
3. Inter-laboratory Agreement. The agreement test is performed when the white calibration tile supplied with the test instrument is traceable to a standards laboratory other than NRC or NIST. This extension of the validation test measures differences in the photometric scales between the laboratories on which traceability is based. Based on the results of recent beta tests, this systematic error may significantly exceed the statistical uncertainty of the SRF measurements.
4. Instrument Revalidation. Repeating the validation test provides a basis for tracking instrument performance and for checking the user's methods for storage and maintenance of the transfer standards.
5. White Calibration Tile. If the white calibration tile supplied with the test instrument is translucent, significant measurement errors may result. Provided that LAV and VSAV sample ports are available, the part A set may be used to diagnose this problem.
6. Translucency Sensitivity. The part A set may be used to measure the sensitivity of the test instrument to SRF errors that result from lateral diffusion. This test requires the use of LAV and VSAV sample ports. For more details on translucency, refer to the blog "Color Measurement Accuracy: Translucent Materials"
7. OnColor Profiler®. Profiling improves inter-instrument agreement in a multi-instrument environment. This may be accomplished using the combined parts A and B standards together with CyberChrome's OnColor Profiler software. Part B of the tile set adds 16 more chromatic colors to better map the color gamut. For more information on the benefits profiling offers, read the white paper on this topic.
The author of this article is John W. Root Ph.D. of Mt. Baker Research who can be reached via email at jackroot@mtbakerresearch.com.
Posted by Elaine Becker on Wed, Apr 28, 2010
CyberChrome Inc was an exhibitor at the recent American Coatings
Show in Charlotte, NC. Featured products included OnColor Profiler for improving inter-instrument agreement and the OnColor Suite of color management software for quality control and color formulation.
According to the press release from the American Coatings Society, "With 328 exhibitors and about 6,700 overall participants (2008: 331 / 5,600), the second edition of the American Coatings Show & Conference was hugely successful as the highlight event of the US paint and coatings industry. The combination of trade show and conference, held April 12-15, 2010 at the Charlotte Convention Center, North Carolina, thus once again exceeded all expectations."
Attendees came from not only North and South America, but there was a strong presence from Asia as well. Visitors at the CyberChrome booth included many US companies but also companies from Canada, Mexico, India, China, and other Pac Rim countries.
Interest in instrument profiling was high as companies struggle to manufacture to the same electronic color standards with tight color tolerances around the world. OnColor Profiler helps to meet the objective by providing much tighter inter-instrument agreement and allows them to meet the rigid color tolerances demanded in today's market.
Many larger companies are also interested in placing color matching systems at their distributor locations where they can match their own custom colors and reduce the burden on the color lab at the main facility. It also allows distributors to turn around custom matches in a much shorter time. CyberChrome's Match Express software provides an affordable and easy to use software package for distribution locations.
While attendance was "decent" at this show, exhibitors and attendees both wonder about the future of trade shows such as this one. With internet meetings, webinars, and the high costs of travel, it seems like fewer and fewer people attend these shows. There is still much to be said for face to face meeting, ralationship building and the social interaction that happens at events like this. What are your thoughts on attending trade shows in the future?
Posted by Elaine Becker on Thu, Apr 08, 2010
This blog article was written by Dr. John W. Root of Mt. Baker Research:
A translucent solid is not perfectly opaque. Part of the light incident on it penetrates the surface where it undergoes internal scattering and lateral diffusion away from the entry point. Both processes reduce the intensity of reflected light.
Because of lateral diffusion, the reflectivity of a translucent solid decreases as the size of the instrument's sample port is reduced. This effect causes systematic errors in measured spectral reflectance factor ("SRF") data. The magnitude of these errors depends on the following: (1) Instrument geometry. (2) Characteristics of sample surface. (3) Sizes of illuminated and measured areas of sample.
Measurement of Translucency
In commercial spectrophotometers that support diffuse illumination, the entire exposed surface of the sample is illuminated and an optical system controls the area viewed by the detector. Over-illumination is achieved by configuring the viewed area to be smaller than the illuminated area. Experiments in which over-illumination is varied can be used to measure the fractional reflectance losses ("FRL") that result from lateral diffusion. The author recently used this technique to measure FRL values for many ceramic tiles, glasses, and plastics.
The X-Rite ColorEye 7000A ("CE7000A") spectrophotometer supports a wide range of over-illumination. Maximum over-illumination is achieved with the LAV/VSAV configuration in which the LAV sample port is combined with the VSAV lens setting. The VSAV/VSAV configuration minimizes over-illumination.
The typical FRL results reported below were calculated from SRF data measured using the LAV/VSAV and VSAV/VSAV configurations of a recently purchased CE7000A (S/N 37132651108). The success of this method requires that the instrument's white calibration tile exhibit negligible translucency. This was the case for the author's new CE7000A, but not for his 2nd instrument (S/N 37116190602).
Translucency in Transfer Standards
The author's tests demonstrated that many optical materials exhibit translucency. For the FRL values listed below the 2σ standard error of estimate is ± 0.03%.
Typical Values: White Carrera® glass, 25.6%. Extruded Teflon®, 22.9%. White Vitrolite® glass, 18.9%. Ceram red-orange 99/1 tile, 8.98%. Sintered PTFE powder (Fluorilon® and Spectralon®), 3.6% - 2.9%. Ceram red tile, 3.14%. MC-20 Russian white opal glass, 3.13%. Ceram orange tile, 3.03%. Ceram yellow tile, 2.52%. X-Rite white calibration tile (S/N 37116190602), 1.43%. Konica-Minolta CMA103 white tile (S/N 18776042), 0.90%. X-Rite white calibration tile (S/N 37132651108), 0.00%.
Although FRL values may be measured using other instruments, the results will depend on the translucency of the instrument's white calibration tile as well as the dimensions of its LAV and VSAV sample ports.
Comparisons of SRF data measured using instruments with large vs. very small sample ports should be based on opaque transfer standards. If the standards are translucent, inter-instrument agreement cannot be achieved. Instrument profiling cannot mitigate the errors that result from the following sample characteristics: (1) Thermochromism. (2) Translucency. (3) Surface inhomogeneity.
The guidelines listed below are based on the sample port sizes of the CE7000A. They are recommended for transfer standards that are used for testing and profiling instruments in the diffuse SCI geometry. The FRL values should be less than 3.5% for instruments that support over-illumination and a LAV, MAV or SAV sample port. For instruments that support a VSAV sample port, the values should not exceed 1.5%.
The author of this article is John W. Root Ph.D. of Mt. Baker Research who can be reached via email at jackroot@mtbakerresearch.com.
Posted by Elaine Becker on Thu, Jul 16, 2009
So many color disputes arise these days because color instruments don't necessarily read the same. Electronic color standards are widely used and shared within a supply chain and have many benefits, but if all of your instruments are not regularly monitored and are known to read the same, then problems can arise.
Many users assume that since they do a daily calibration on their instrument, their readings are correct. And if they are correct, then they must match every else's. That's not usually the case. Spectrophotometers from different suppliers may read color differently. Even with the same model from the same supplier, significant differences can be found depending on the age of the instrument and how well it is maintained.
In order for electronic standards to "work" within your supply chain, you need to be able to recall a stored standard, measure the actual stored standard on another instrument and have a resulting DE of 0.15 or less. The number of 0.15 is dependent on how tight your tolerances are. If you are trying to supply a color match that is < 0.5 DE, then you certainly don't want to have half of that deviation taken up by lack of inter-instrument agreement. A good rule of thumb is that no more than 25% of your tolerance should be given up to instrument variables (such as INTER-INSTRUMENT AGREEMENT, sample repeatability, and instrument repeatability). So if your tolerance is DE=1.0, then you can live with measurement uncertainty of up to 0.25 DE. If your tolerance is DE < 0.5, then you can live with an uncertainty of no more than 0.125. So as tolerances get tighter and supplies get more critical of color, INTER-INSTRUMENT AGREEMENT becomes more important. Instrument profiling can help you achieve the INTER-INSTRUMENT AGREEMENT that you need in order to meet these tight tolerances.
One advancement in color technology in use today is instrument profiling. Instrument profiling is used to make a population of spectrophotometers read to within a tighter specification of each other. A master instrument is used as the reference point and all other instruments are "cloned" to match this master instrument. A complex set of equations is used to profile or "correct" a target instrument so that its spectral data mimics that of the master. After profiling, all data taken on the target instrument is now corrected to match the master. The result is much tighter agreement between instruments which leads to fewer disputes over whether the color match is acceptable and faster acceptance and approval of submits.