Inter Instrument Agreement – What are the practical implications?

What does Inter or Intra Instrument agreement mean? It is the ability of instruments of the same type (Inter) or of the same model (Intra) report very closely correlated results.
Why is this important? Groups of instruments within one site or one company nationally or globally, or between customer and supplier can agree without doubt that one is more correct than the other.

Measuring Sample colours to Target Masters is a pretty straightforward procedure, as long as you are looking at a single instrument at a single site for local quality control. As you are measuring colour difference rather than actual colour, if the instrument drifts with time, as long as you have a current Target Master, your results will be fairly constant.

The situation becomes much more complex when you need to compare Target Masters on a number of Instruments at one or many sites.  In a previous Blog What do we see when we see L*a*b?” we mentioned that comparing colours requires not only knowing the L*a*b (For instance) values, but also conditions under which these were obtained. 18 conditions were enumerated, and we did not go into any depth as to what Inter Instrument Agreement meant for the multiple user.

There is an old manufacturing saying that says:” In Theory, there is no difference between Theory and Practice. In Practice, there is!”

Colour Space Values (e.g. L*a*b) are theoretical unless accompanied by all contextual data as well. It is not enough to assume that using the same instrument is enough. ALL of the settings have to correlate.

We were doing some training with a customer in November, and we happened to have two identical instruments (Konica Minolta CM700d) and our Bench Top equivalent the Konica Minolta CM-5 as well. The customer uses all three instruments to compare food ingredient colours around Southern Africa. While discussing the point of Inter Instrument Agreement, we noted that one of Konica Minolta’s unique properties is the high degree of agreement between instruments, both Intra (Same model) and Inter (Same type – different model). This means that when results are shared around the country, it is not too critical which instrument was used, as long as the setup and applications are identical.

Customers being customers, my guest suggested I demonstrate there and then that this was so.


We first ensured that all our settings were identical, and then proceeded to measure a sample one after the other. The top left portable is about 4 years old, the top right a few weeks old and the bench top about 18 months old. All are calibrated and certificated so no problems were expected.

I took a photo (Even Spectros like Selfies!) and if the reduced image is hard to read, the actual colour space numbers are repeated here below. Needless to say, our customer was impressed with this unrehearsed outcome. (You can enlarge the image by clicking on it)