The information engraved into the grooves of the LP records is of microscopic proportion, therefore when we talk about tonearms, we talk about microscopic movement.

The standard dimensions of an unmodulated (silent) record groove are shown in the accompanying cross-sectional diagram 1, which represents a magnification of about X260. (A micron, is one thousandth of a millimeter.) As viewed from the front of the cartridge (equivalent to the stylus travelling into the paper), the left groove wall carries the left channel, and the right groove wall the right channel.

The precise stylus cross-section chosen to fit the groove varies between stylus types, but is chosen as a compromise of the same factors. The vertical contact between stylus and groove wall should be as long as possible, but must take into account the narrowing of the groove on vertical modulation. As far as possible both the top edges and the bottom of the groove are to be avoided; the top edges and groove bottom are often damaged during cutting and pressing (the latter by deliberate 'dehorning' of metalwork), and the groove bottom accumulates dirt.