I would say re sale value in un calibrated and neglected condition is low. It can be a very time consuming job to bring them back to life after many years of neglect. They need setting up and calibrating by a pro. I’m sure there are very few that @Lodekka has been unable to bring back to life. Once brought back to life, they should be good for many many more yearsWe have a metal one in the shed, also I have a wooden / bakelite one that I bought in a junk shop many years ago. Have they any value now?