In diameter, to a total resistance of zoo ohms. The actual current required to work the instrument is 3.3 milliamperes (equivalent approximately to the current given by 1 Daniell cell through 3300 ohms), but in practice a current of to milliamperes is allowed.
40 ohms (or 900 ohms when worked from accumulators), and the instrument is worked with a current of 400 milliamperes (25 milli British Post Office.
The standard relay will work single current with a current of 3 milliamperes, though in practice about 10 would be used.
Worked double current - that is, with the tongue set neutral, having no bias either to the spacing or marking side - the relay will give good signals with 12 milliampere of current, though in practice 10 milliamperes are provided.