Proper Sample Alignment
The model 939, as well as many other X-Rite handheld instruments, includes a alignment guide in the instrument shoe (base plate). This guide includes a hole through which the measurement is taken. For accurate measurements, this opening should be filled with the sample color you are measuring. If the sample is too small to fill this opening, inaccurate measurements can result as the instrument may be including the surrounding area or color in the measurement taken.