well I got one of those from the 80's but I destroyed the acrylic knob. I have been meaning to polish out a groove in there so I can glue on something, or to find a replacement.
Check for leakage from the 12V battery in there for Ohmmeter mode.
And its adjusted by replacing resistors IIRC. That thing is pretty stable and small, I don't think I saw any trimmers in mine (but its for Bell)
Yours has a knob on the bottom, mine has more of a watch dial.
I think I have a 318 though. Maybe you can just get parts for that still, I never looked. I had a fun time polishing it with tooth paste lol
It has a potentiometer for ohms, but I don't think you can do anything with the voltage dividers other then replacing resistors
https://www.parts-express.com/pedocs/manuals/391-040-triplett-310-manual.pdf