1. The first few ZC1 Mk-1's were fitted with two meters. One, a 500mA thermocouple type RF Meter, was discontinued in later sets because of the difficulty in obtaining large quantities of suitable meters. Although such a meter is useful it is not essential and it was found expedient to discontinue fitting them.
2. The meter used was a Standard DC milliampere meter fitted with a small internal thermocouple. The thermocouple permitted the RF output of the set to be measured and displayed.
Not all meters labeled as RF Meters contain thermocouples, many such meters from this period used external thermocouples.
The low power and delicate thermocouples used are easily overloaded and damaged.