To provide matching between the Wireless Set 19 A Set and the Antenna a Variometer is used.

As the 19 set was designed for generally short range communication at a low power it was not deemed required to design an antenna tuning unit that would use a roller inductor design, as this would use up precious metal's. So an antenna coupling design was the outcome in the form of a Variometer.

If the 19 set was configured as a high power deployment, there is a roller coaster tuner, that externally looks the same as the common Variometer, but internally it is a roller inductor, the main external clue being rather than a single open dial indicator, it has two small round windows above the tuning knob.

Variometer's were manufactured by all countries engaged in 19 set production, the design was not generally changed and the main differences between manufacturers was the final external finish. US production was a crisp dark green crackle finish, Canadian's brown paint and the British generally grey or green paint.

The variometer was either mounted to the side of the power supply with a bracket or installed near the radio on the vehicle itself. On the rear a plate is provided so the output type can be changed, based on the type of installation. Non-fixed installations having a terminal post, fixed armoured installation a spigot. US produced Variometer's came from the factory with a blanking plate on the rear, which was changed on installation.

Note: If the control knob is hard to turn, generally this is the grease on the tuning mechanism behind the knob having dried out and is an easy fix.