Unless rubbing your nipples is part of your job, anyway.. Andractim testosterone gel is a topical gel, which comes in a tube, containing 80x 25mg doses of DHT. Absorption rate is going to be similar to testosterone gel, or roughly 10%, so youre applying 2.5mgs of pure DHT to your nips every time you use this stuff.
Servos are also used in in-line manufacturing, where high repetition yet precise work is necessary. Of course, you don't have to know how a servo works to use one, but as with most electronics, the more you understand, the more doors open for expanded projects and projects' capabilities.
In the context of audio circuits, a servo is usually an active element used in feedback in order to null or reduce an amplifier's offset voltage. Consider Fig. 1. On the left is the schematic for a differential operational amplifier (op-amp). On the right is the symbol usually used to represent this type of circuit.