A colour matching experiment of the maximum-saturation type has been conducted on a group of five observers. The sources of uncertainty in its outcomes were identified and analysed. The variability introduced by the instrumentation was found to make a significant contribution to the total data variation for a single observer. Variability for a single observer, in its turn, contributes significantly to the overall observer-related variability. The CIE Standard Deviate Observer significantly underestimates the variability of colour matching according our study. The choice of the primary lights has an effect on the variability of colour matching. The results generally agree with previous findings by other researchers, although there are some differences in detail.