Volume pot dating
Figure 2 - Some Examples of Knobs Of these, only one deserves special mention - the one on the left.This is a multi turn vernier readout (analogue in this case) for a standard pot.For manufactured products, it's probably because the stamping press simply doesn't have the character available.If you see 'W' or 'ω', it often (but not always) means ohms.
They are used for 'trimming' the value of a resistor, and are commonly used for calibrating instruments, setting the bias current on power amplifiers, and a host of other areas where a circuit with fixed values cannot be relied upon to give an exact gain, output voltage, or current.Apart from the different body shapes and sizes, there are also many 'standard' mounting hole and shaft sizes.Probably the most common of all is the one in the centre of the picture. This uses a 10mm (3/8") mounting hole, and has a 6.35mm (1/4") shaft.Figure 1 shows an array of conventional pots - both PCB and panel mounting.Figure 1 - Some Examples of Pots Note that these are not to scale, although the relative sizes are passably close.
More compression leads to lower resistance, and vice versa.