Potentiometers are variable resistors (apparently invented by Thomas Edison in 1872) and pretty much every electric guitar ever built uses them for its volume and tone controls. The basic rule of thumb is that we use 500kohm pots for humbuckers and 250k pots for single coils. Lesser-used values are 1meg-ohm (1,000k) where you want to maximise the brightness, and 300k where you want to sit between those two standards. These are nominal values in that pots, such as capacitors or resistors, have a production tolerance expressed as a percentage. So a 500k pot with a 10 per cent tolerance could actually measure anywhere between 550k and 450k to be in specification. And because, in theory, the higher the value, the brighter the sound, you can use the actual measured value to subtly ‘tune’ the pickup.
Even if you know next to nothing about pots, anyone who has owned different guitars over the years will have noticed that they can all differ subtly in their feel and the way they raise and lower your volume. Some pots have a pretty fast rise with most of the perceived volume increase happening between 10 and 7 on the control – which is great for fast volume swells or where you need to go from ‘lead’ to ‘rhythm’ volumes with the minimum of travel. Other pots, however, have a slower rise and sound more even from off to full-on. This is referred to as the taper and numerous companies advertise their pots with a ‘custom’ taper, or even a ‘vintage’ taper.