Color code variations

Three band resistors

Very long ago, back in the 20th century, it was assumed that all resistors were 20 %, or worse, and thus didn't need any tolerance marking. Also, since the tolerance was so wide there was no need for more than two significant digits. These resistors are in the E3 or E6 series. If you stumble on one of these, call your local museum.

Four band resistors

Mankind eventually learned to manufacture 10 % or even 5 % resistors and a tolerance marking had to be invented. There were still no need for more than two significant digits, and therefore four color bands did the trick. These resistors typically are in the E12 and E24 series.

Five band resistors

Engineers' appetite for precision led to the development of 2 % and 1 % or better resistors, and in order to keep the logarithmically constant difference between consecutive resistance values another significant digit had to be employed. But engineers also developed tools to paint tinier color bands, so that was not a problem. These resistors belong to the E48, E96 and E192 series.

Six band resistors

Now that tolerances were in the sub-percent region, another factor had to be accounted for, namely temperature coefficient. Well, why not just throw in yet another color band? Good idea. Here it is.

There are also other uses of the sixth color band, for instance quality codes. These are, however, not well standardized and are therefore not part of the color code calculator.