The 3 Ratio P.O. Box has sixteen non inductively wound coils 1, 2, 2, 5, 10, 20 , 20, 50, 100, 200, 200, 500, 1000, 2000, 2000, 5000 ohms & two proportional arms each with coils of 10, 100 and 1000 ohm. Also incorporates infinity gap.

The 4 Ratio P.O.Box has sixteen coils as above and three proportional arms each with coil of 1, 10, 100 and 1000 ohms.

Also incorporates infinity gap.

Heavy superior quality double brass terminals are provided and panel is clearly engraved with the normal resistance values.

Two spring keys having good contact for battery and galvanometer is also provided.

The whole system is contained in a superior quality teak wood box.

ZES 240. P.O Box 3 Ratio :

Consisting of 12mm thick rectangular brass block. Coils are wound with constantan/ manganin coil. Having accuracy 0.1% for Constantan coil & 0.05% for Manganin coil.

ZES 241. P.O. Box 4 -Ratio :

Consisting of 12mm thick rectangular brass block. Constantan coil. Accuracy 0.1% & 0.05% Maganin coil.