Why the microscope?
Short answer: the microscope allows better quality control.
The microscope is a relatively new addition to the tools of the stonesetter. For centuries, the best setters have made exquisite ornaments with only the use of simpler magnifying tools. The jeweller’s loupe with around 10x magnification is a well know example. But there are also magnifying spectacles that provide 2x to 4x enlargement. The setter uses these to check for the minute details that separate average from excellent work.
The microscope improves on this in two ways. It offers considerably improved magnification (20x to 30x) while keeping the craftsperson’s hands free. So the microscope is a superior tool for checking quality of workmanship. It is in itself no guarantee for perfect execution. However, it does make it a lot easier for the craftsman to deliver high quality results.