In order to scale the count values to a reasonable number of digits, Troxler devices use prescale factors when performing measurements, standard counts and any other diagnostics count. In other words, the count that a gauge displays is the total number of ionization events measured by the gauge divided by the appropriate prescale factor. The prescale factor is typically not needed by the gauge operator. However, the ASTM standards D 6938 and D 2950 give a formula, to check the stability of the standard counts, which requires the use of the prescale factor. The prescale factors are listed below: For Troxler Models 3401, 3411, 3430, 3430 Plus, 3440, 3440 Plus, and 4300 devices, a prescale of 16 is to be used in the formula when a 4-minute standard count is performed. For Troxler Models 3450 and 4640 devices, a prescale of 8 is to be used in the formula when a 4-minute standard count is performed.