Can you help identifying these parts?

[Dcalaby]

I am wondering if anyone can help me identify the part shown in the pictures attached.
I only have the following information from the box as follows:

Resolver Ball 2"
Single No 2 Mark 1

Manufacted by G.E.C
August 1955
D.O/6/insts/7904/cb32b
PKD S.E.1. FC/misc/647H

Any help in identifying this part and it's use would greatly appreciated, so that I can find the right home for it and hopefully the 6 (sealed and boxed) others I also have.

thanks in advance.