DP-1 carbon and wire cladded ring resistors
Only DP-1s from 1975 with serial numbers 60xxxx and above have factory installed wire cladded ring resistors, similar to the ones in the DP-11s. The earlier carbon ring resistors wear out much quicker than the wirewound ones. At their end-of-life, the DP-1 meters tend to be jumpy or stuck at each end. The carbon ring resistors can be cleaned, and brought back to life again, but they will eventually wear out and become jumpy again. The wire cladded ring resistors, however, can last a life time. Some DP-1s had their carbon ring resistors replaced with the wire cladded ring resistors, and they will last a life time too.
DP-1 with carbon ring resistor DP-1 with wire cladded ring resistor