If you work with robotics, avionics, an other fields that use angles you might just run into one or more these things. They are motor like devices that can transmit, or receive angles called Synchros in older aircraft they are used in pairs,
a transmitter (tx) and a receiver (rx) . As you can see in Figure 1 by moving CG the CR will move exactly in step with its counter part. This figure is from Synchro Application Guide. There is lots more information in the Synchro handbook.