Hi Frank,
I would agree with the book choices but wobblers are not only for mills. I use one for centring jobs in the four jaw chuck.
Mark your centre with a fine pop, mount the body of the wobbler in the tailstock chuck and set the point in the centre pop. Rotate the chuck by hand and set the job in the chuck for no run out, use a test indicator to check your run out if it is critical, otherwise your eye is pretty accurate – you are looking for no sideways movement of the wobbler – er, no wobble – to set the job on centre.
If you have one of the sets that are common now, the different ends are for different size centres and for finding the edge of a job – same principal as for centring, but you use the barrel-ended wobbler. Set the machine (lathe or mill) going and watch for the wobbler to straighten as you bring the job up to it, When it is straight then the machine head is dead in line with the edge (assuming that you have a good set and the barrel is concentric with the shaft. You then zero your dials and work coordinates from that datum.
As Nobby points out (I think), a wobbler is east of the pond, a wiggler is west of it.
Andy (I will duck down below the parapet now)