These procedures are shown below. It often happens that the standard units for some quantity is not convenient in a particular case. There is an established series of values of resistors, only values with certain digits are manufactured. Tolerance of the resistance varies - resistors are mass manufactured, so some variations are hard to avoid. Resistors generate heat.
Resistors have a wattage rating.
Wire wound resistors have their value written on them. The Resistor Colour Code allows to read the values of resistors. The procedure is as follows. You should ignore the colour of the resistor body. Most resistors have three coloured bands close together at one end and one single band at the other.