I was given this tool some years ago by a machinist specialising in gears and splines that didn't know what it was.
I thought it might be of some use on a mill but haven't used it yet.
The tool was manufactured by the Monarch Tool Company Ltd, Kirkheaton, Huddersfield, UK.
Internet searchs found no reference to the company.
The tailstock is spring loaded and when the headstock spindle is rotated anti-clockwise as
you look from the tailstock moves towards the tailstock. It sit on a graduated swivelling base.

http://metalworking.com/DropBox/monarchmysterytool.txt
http://metalworking.com/DropBox/monarchmysterytool.jpg

Any thoughts as to what its purpose is would be appreciated.