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The resistor color code indicates the electronic value of a resistor. Manufacturers devised the universal electronic color code rating system in the early part of the twentieth century because the bands of color were much easier to read on a small resistor than tiny print, and were also cheaper to produce. Each color represents a different rating, and by reading the resistor color code bands from left to right a person can determine the precise value of any resistor. Resistors are always rated in ohms and can have anywhere from two to five color bands. Three or four bands are the most common.
In order to read the value of a resistor color code correctly, the resistor must be oriented so that the silver or gold color band is on the right. This band gives the tolerance of the resistor. Tolerance refers to the range of variation between the true value of the resistor and its design specifications. If there is no silver or gold band, the band closest to one of the leads will be considered the first one.
A gold band represents a tolerance of +/-5%, and a silver band represents a tolerance of +/-10%. If no tolerance band is present, the tolerance is +/-20%. There are some resistors with smaller tolerances, but gold and silver are the most common tolerance band colors.
The first two color bands on the resistor represent its two-digit number, called the significant numbers, and the third band is the multiplier. A multiplier tells which power of ten the first two numbers should be multiplied by. The fourth band shows the tolerance. For example, if the resistor has color bands of yellow, violet, red, and gold as one reads from left to right, the first number will be 4, the second number will be 7, the multiplier will be 100, and the fourth band of gold means the tolerance will be +/-5%. In other words, the resistor color code shows the component will have a rating of 4,700 ohms, and with the tolerance of +/-5% the actual value might be anywhere from 4,465 ohms to 4,935 ohms.
The colors in the resistor color code chart are arranged in the same order as they are in the color spectrum, with black on the far left and white on the far right. These values are recognized internationally. Charts showing the numbers and multipliers represented by each color are available online.