Though resistor marking may not display their value outright, most resistors are marked to show what their resistance is. PTH resistors use a color-coding system, which really adds some flair to circuits.

 

Through-hole axial resistors usually indicate their value by color-band system. Most of these resistors will have four bands of color circling the resistor, five band and six band resistors are also can be found

 

In the standard four band resistors, the first two bands indicate the two most-significant digits of the resistor's value. The third band is a weight value, which multiplies the two significant digits by a power of ten. The final band indicates the tolerance of the resistor. The tolerance explains how much more or less the actual resistance of the resistor can be compared to what its nominal value is. No resistor is made to perfection, and different manufacturing processes will result in better or worse tolerances. How can we  tell the first band from the last band? The last tolerance band is often clearly separated from the value bands, and usually it'll either be silver or gold.

 

Five band resistors have a third significant digit band between the first two bands and the multiplier band. Five band resistors also have a wider range of tolerances available. Six band resistors are basically five band resistors with an additional band at the end that indicates the temperature coefficient. This indicates the expected change in resistor value as the temperature changes in degrees Celsius. Generally these temperature coefficient values are extremely small, in the ppm range.