The problem with those you have recaliberate the handheld each time you adjust the spindle speed ie adjust for one setting then take another reading for another setting.
....
Can you explain what the difference is between using a rear mounted tool post as opposed to running a conventional set up with the lathe in reverse and the part off tool mounted upside down?
Under flourescent lights, it reads 3600 RPM even with nothing moving.
Ok if its a cheaper wars yer after...
http://cgi.ebay.co.uk/New-Digital-L..._Measurement_Equipment_ET&hash=item43a566a1af
But yer can't beat a dedicated spindle counter.