Thanks NoTransisitors, Pictures of the booklet would be great as info on these is seems to be pretty scarce.
Mine doesn't have the little drawer on the side like I've seen on others, but i finally got this open. Opened by removing 'guts' from bottom of shell after a lot of fiddling around.
Inside was the scale, battery/contacts for top 'lens piece', a tiny mercury filled tube and out of place, a 1" machine screw with 3 washers. The screw and washers just fell out so not sure if they served a purpose. Battery appears to be soldered in place and either glued in place or corroded. (goopy opaque amber stuff holding hostage, as opposed to the usual white chalky stuff from leaky alkalines, with a small lead soldered on the side of the battery)
Will try to fix it, not because of any practical purpose, but because my audio ocd can only stand so many non working things in the house, lol.