Resistors that were used in the Amstrad use a colour coding system to identify their resistance value. This document describes this colour coding.
Modern resistors are surface mount and use a single colour to define the resistance. This document doesn't describe the colour code for these resistors.
On the body of the resistor there are 4 coloured rings. The colours must be read in the correct order for the correct resistance value to be determined. The first ring is close to one end of the resistor, the last ring is much furthur away from the other end of the resistor.
The first two rings specify the first 2 digits of the value. This value is a decimal number.
The third ring specifies a multiplication factor. The resulting resistance is defined by the value and the multiplier.
The final ring is a colour which defines the "tolerance".
Value (first two rings):
Multiplying factor (third ring):
Tolerance (final ring):
In the picture above the coloured rings (in order) are:
yellow, magenta, black and silver.
Yellow and magenta give a value of 47, with a multiplier of 1.
The silver ring defines a tolerance of 10%.
The final resistance is therefore: 47ohms/10%