Tuning Indicators
Tuning Indicators or 'Magic Eyes' are small cathode ray tubes that indicate signal strength by the deflection of an electron beam on a phosphor target. The phosphor is almost always green. They sometimes also include a triode to amplify the indicated signal.
Counters
Nixie Tubes and other numeric indicators
'Nixie' tubes are usually neon lamp decimal indicators with cathodes shaped to form the individual digits. There are some specials which have other symbols. 'Nixie' is a trademark of the Borroughs Corporation. The primary advantage of the Nixie tube, apart from the aesthetics of the numeral shape, is that when rapid jitter between digits occurs it is often easy to determine which two digits are involved. This is not the case with the later seven segment displays which often produce an '8' when alternating between two digits.
Nixies were used in many different indicating applications, often in measuring instruments like voltmeters or frequency counters, but also in tills and clocks. Current use, except for historic pieces, is more or less confined to clocks.
Also included here are other numeric indicators which use filament or vacuum flourescent technologies.
Dekatrons
Dekatrons are decade pulse counters which indicate the current count by means of a neon glow around a pin. The glow transfers from pin to pin on each input pulse. They can be used as decimal dividers by taking the pulses from one pin as the input to the next stage.
They were some of the earliest fast counters, capable of speeds in the tens to hundreds of kilohertz, several orders of magnitude faster than the alternative relays. They were frequently used in radiation or other decade counters, but also in some early decimal calculators.
