I have a Starrett 98 8" level I want to use for, what else, levelling my lathe and it performs exceedingly well. I also have a 98-6" level in need of help, it will not level. In the past, to test levels, I'd do so rotating them 180. This one will level in 1 direction but is quite far out when rotated. I would like to adjust it, it has the screws for this but what to adjust, it's level unidirectional. Would the glass be defective, all else looks well cared for. Thank you for your help.BB