RESISTOR COLOR CODING

A resistor is a passive two-terminal electrical  that implements electrical resistance as a circuit elements. Resistor is used in electrical circuits to manipulate the current flow. 

The colored bands around the body of a resistor indicate its value in ohms and its tolerance if there are four bands. As the drawing shows the first band represents the first digit of the value and the second band is the second digit of the value. The third band represents the number by which the the two digits are multiplied. A fourth band of gold or silver represents a tolerance of +-5% or +-10% respectively. If no fourth band is shown, the tolerance is assumed to be +-20% of the indicated value of resistance.

Resistor color code table

The physical size of a composition resistor is related to its wattage rating. Size increases progressively as the wattage rating increases. The diameters of 1/2 watt, 1 watt and 2 watt resistors are approximately 1/8 in., 1/4 in., and 5/16 in., respectively. 

Example:

Reference:

Electrical and Electronics drawing, 2nd edition (Charles J. Baer)