20 Optical recognition machines read the postcodes and automatically convert them to phosphor dots
. These are in turn read by the sorting machines which handle correctly-addressed and postcoded letters 20 times faster than any manual sorting system.
Dan Cifelli, president of DZ, compared this to a cathode ray tube where the television image is created by scanning phosphor dots
with an electron gun.
This is the distance, measured in millimetres, between two phosphor dots
of the same colour, the shorter this distance the finer the image the tube can display.
Dot pitch is the amount of space between the individual phosphor dots
on the picture tube.