Use Kodak photo lens cleaner or eye glass cleaner. The gauge glass is coated...
Posted by NexxTT on 2000-08-28 21:44:55:

In Reply to: Any recommendations for cleaning the glass surfaces of the gauges? Thanks. posted by dmf on 2000-08-28 17:17:06

perhaps an achromatic coating, but it is subject to damage from the wrong cleaner. Also use a soft cotton cloth or eye glass cloth to clean so as not to scratch the glass or particularly, the coating.