The article has investigated a model based on the geometrical distribution and connecting a probability of determining the reference value of a measured quantity with m interlaboratory comparison participants. We have conducted an analysis of the dependency of the probability of determining the reference value of the measured quantity on the number of additional laboratories introduced into a group of comparison participants. On the base of this analysis, recommendations are given for a reasonable choice of the number m at a given elementary probability of determining the reference value for a single laboratory that are ranged from 4 to 10-15. As a rule, at this amount of participating laboratories, including new participants into the comparison group does not produce a positive effect.