have you lubricated it? if so what with?

I have rebuilt a couple of dial gauges an found they work better with no lube IMHO

Though it might only need a clean and a tiny drop of light oil, an old DTI could also be worn, or more likely, the innards are bent due to being bumped or dropped.   A powerful loupe might see the damage, better a microscope.  Small flaws matter to delicate instruments working in the tenths region.

Maybe bad maintenance in the past.  Clocks are famously damaged by over oiling.   The oil attracts dust and becomes abrasive, and then gums up.   The mechanism literally grinds to a halt, and then the bearings have to be replaced.  The old ones have enough slop to upset the gears.

How elaborate was the clean?  Clocks and watches are stripped down completely and the parts put through an elaborate sequence of agitated chemical cleaners, and inspected for damage, especially the pivots, before reassembly.  Iffy parts are replaced.   I think a tenths DTI would need a similar deep clean.

Dave

Thankyou for this thread – I have a DTI with reluctant return action so will take that advice, too!