5. Mistakes to avoid

5.1 Don't confuse an MRE with an MRC

MRC producers indicate on their certificates, with a few exceptions, that an MRC does not have to be used every day, for example to build a control chart. On the other hand, if the calibration of an X-ray fluorescence spectrometer has to be carried out using reference materials, then these are solid, very stable, long-lasting materials, such as rocks, which can be used regularly.

But as soon as we enter the realm of fragile or biodegradable measurands, this approach is totally unsuitable.