Musical tuning
When a violinist tunes his instrument he is making sure that his four strings are tuned perfectly to G, D, A and E.  Each string is wound around a peg near the top of the scroll, so that turning the peg changes the tuning.  He may also have “adjusters” or “fine tuners” which are at the other end of the string where it is attached to the tailpiece.  The adjusters make it easier to make small changes to the tuning.  The violinist will make sure that the A is in tune, then the A and D can be played together so that they are exactly a fifth apart, then the D and G and finally the A and E are compared.