mostly equidistant, inter electrode distance 43 to 68 mm (given a head circumference of 58 cm).
This electrode arrangement resembles a “15%-System”, covering the largest possible area recordable from caps. In 40-Channel-Amplifiers (e.g. Nihon Kohden or NuAmp) still further channels are available. They can be used to place anatomically defined inferior electrodes, as recommended by Professor Scherg for source analysis/epilepsy diagnostics, or for polygraphic channels.