Gage blocks are graded according to a number of national and international standards. The grade designation will depend on the date of manufacture, reflecting the standard in effect at that time....
When purchasing a used microscope, E bay Lab X are a good source, used microscope dealers are also if the has a competent service department. Get a guarantee at least 30 days specify that the focus be smooth...
There's always an element of risk when buying anything without actually seeing it "in the flesh" (actually being able to examine it in person)and therefore buying items on-line can often result in...