The thermal G G detectors are especially useful for the purpose of quantitative measurements, because they indicate the true effective or square root of mean square value of the current or train of oscillations passing through the hot wire.
The capacity of the condenser is then altered until the maximum current, as indicated by a hot wire ammeter, is produced in the circuit.
Hot-wire ammeters are, however, liable to a shift of zero, and means are always provided by some adjusting screw for slightly altering the sag of the wire and so adjusting the index needle to the zero of the scale.
From this it follows that hot-wire ammeters are generally not capable of giving visible indications below a certain minimum current for each instrument.
Hot-wire instruments working on the sag principle can be used in any position if properly constructed, and are very portable.
