I wonder if anyone would know the origin of the Resistor Color Code.


The color code was developed in the 1920's by the Radio Manufacturers Association (RMA) as a three band code for resistor values. The three bands were more compact than the number value because the third band represented the number of zeroes. For example, 250 000 Ω was reduced to three bands. In addition, color bands remained visible in whatever position a resistor was soldered, whereas a stamped number value could be out of sight. The fourth band, representing the tolerance, was added later.

Initially the three colors were not three separate bands, and there was no neutral background color. Instead, they were the body color, the tip color and the dot color, as in the diagram. Identical adjacent colors were allowed. Radio Physics Course, Ghirardi, 1931

The sequence of the central group of colors, ROYGBV, was chosen to match the rainbow mnemonic: red-orange-yellow-green-blue-violet, "ROYGBIV", without indigo because most people do not distinguish, with their eyes, a separate color between blue and violet. The rainbow group is preceded by two low brightness colors, black and brown, representing the lowest digits 0 and 1, and succeeded by two bright colors, grey and white, representing the highest digits 8 and 9. Electrical Engineering Science, Preston, 1960, p.115

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