I believe you are refering to positioning a microscope over a lathe. My background was robotics design, manufacturing engineering and machine design and I use a different approach to making parts. I have made parts this way for so long I do not believe that at this stage in my life I could change even if I wanted to (which I don’t). I admire the artistic skill someone has using a graver but my approach is to form a mathematical construct of the part and cut to the numbers. I have not mounted my microscope over a lathe because in my case it was not necessary. I think Willofiam did and he can provide more information on this matter than I can. As far as measuring extremely small, delicate and high precision parts, I have a UNITRON STAGING MICROSCOPE that can accurately determine the size of a part to 50/1,000,000 of an inch. With this tool I can accurately determine the part dimensions. By using dial indicators on the cross slides I also can accurately determine the cutter location when I machine a part. This also means that the 1st part is exactly like the 2nd part and the 3rd part………the last part.