Thanks folks, useful as usual – I will probably splash out another £10 on one of the suggestions and see what I get.
Dave – I suspect that the battery life issue is the reason that many cheap ones now don't retain zero – and in reality few people who buy cheap callipers care about zero retention. They do care that the ones that arrive when purchased work, and the ones that retain zero may very well go flat in storage/transit.
Bernard – the one I have successfully butchered was definitely not that hard. Cut the jaws off with a hacksaw no problem.
Ady1 interestingly the pictures on the one you link to show a 0.01mm resolution, but the writeup only claims 0.1 resolution – more sharp practice on E-bay?
MC – perhaps when it stops being a project and turns back into a lathe again I might do so. Long way to go however.
Gary – I had that problem with my now butchered calliper – it kept resetting to 5.04mm at zero. A new battery fixed it.
Edited By Peter Cook 6 on 09/05/2021 12:13:14