The 3-ratio Post Office Box has sixteen non-inductively wound coils — 1, 2, 2, 5, 10, 20, 20, 50, 100, 200, 200, 500, 1000, 2000, 2000 and 5000 ohms — and two proportional arms, each with coils of 10, 100 and 1000 ohms.

We are manufacturers and suppliers of the Post Office Box (plug type, constantan and manganin coil), serving Algeria, Argentina, Australia, Bahrain, Bangladesh, Belgium, Bhutan, Brazil, Cambodia, Cuba, Cyprus, Denmark, Ecuador, Egypt, Ethiopia, Finland, France, Georgia, Germany, Ghana, Hungary, Iceland, Italy, Japan, Jordan, Kenya, Kuwait, Malaysia, the Philippines, Tanzania and Uganda.