Because carbon resistors are small physically, they are color-coded to indicate their resistance value in ohms(Ω). The basis of this system is the use of colors for numerical values as listed in table 1-1 and 1-2. In memorizing this colors, remember that the dark color, black and brown correspond to the lowest number, zero and one through lighter colors, to white for nine. The color coding is standardized by the Electronics Industries Association (EIA).
RESISTANCE COLOR BANDS.
This code is the most common system used for color coding insulated carbon resistors having axial leads, as shown above. Color band are printed at one end of the insulating body. Reading from left to right, the first color band close to the edge indicate the first digit in the numerical value of the resistance. The second band is the second digit. The Third band is the decimal multiplier giving the number of zero after the two digits. The resulting number is the resistance in ohms.
As an example as shown in the table the first stripe is Brown for 1, the second stripe is Black for 0 the Green multiplier mean add five zeroes to 10 therefore this resistance value is 10 x 105 or 1,000,000 Ω or equivalent to 1MΩ
If the thirds stripe is black means “do not add any zero to first two figures so if the color is Brown, Black and Black stripes the resistance value would be 10Ω.
Resistors under 10 Ω have third stripe of gold or silver which are fractional decimal multiplier for instance if the stripes of the resistor are yellow, violet and gold multiply the first two digit by 0.1 and if the third stripe is silver multiply by 0.01, so for instance if the stripe of the resistor are yellow, violet and gold the resistance would be 47 X 0.1 or 4.7Ω if the third stripe is silver the resistance would be 47 X 0.01 or 0.47Ω.
Gold and silver are fractional multipliers only in the third stripe. However gold and silver are most often used as fourth stripe to indicate how accurate the resistance value is.
The amount by which the actual resistance can be different from the color coded value is the tolerance, usually given in percent. For instance, a 100,000Ω or 100KΩ resistor with ±10 percent tolerance can have a resistance 10 percent above or below its indicated resistance so when check from multi-meter the reading could range from 90,000Ω up to 110,000Ω value. The inexact value of carbon-resistors is a disadvantage resulting from their economical construction, but in most circuits 5 to 10 percent variation in resistance can be tolerated.