Cambridge University Machin Colour Trials of 1969 - Part 2

Part 1 is here.

The review of the colours was conducted by 39 female members of the Cambridge University Applied Psychology Unit's Research Panel. The members were asked to compare each of the 25 colors with itself and with the other 24 in a series of paired comparisons, making 325 in all. Half worked in daylight, the other half in white fluorescent light.

Each stamp pair was displayed for three-fourths of a second, with an interval of two seconds between pairs. The member wrote S (same) or D (different) for each pair and also indicated whether her judgment was certain, almost certain, fairly certain, not too sure, or guessing.

The number of errors in judging same or different was tallied, and the colours were ranked according to the number of errors in which each colour was involved.

The colour with the most errors was considered the most confusing, and it was eliminated. Further tests were then done with the remaining colours. (Incidentally, the most confusing colour was plum.)

Eventually, the 11 most confusing colours were dropped, leaving 14, which was the number needed for the new decimal series. The 14 tended to be brighter hues, which were found to be less confusing. (The least confusing colour was red.)

Shown above is a portion of the final 14-colour scheme with each colour allocated to one of the decimal values. The complete set of 14 can be seen here. This recommendation was sent to Don Beaumont at the Post Office.

(Ultimately, only 12 values were in the initial set. The 4 1/2p and 8p were not issued until 1973.)

Note: Tony's research indicated that the Research Panel consisted of 39 women. However, the 1972 book Britain in Miniature, produced by the Post Office, indicates the testing was done by 26 women and ten postmen. More about Britain in Miniature soon.

(To be continued)

Larry