Is The Optical Comparator Still Useful
This precision measurement tool is quite capable of accuracies of .0002 in./.005 mm. Time spent practicing with known gages is time well spent. There are some subtle aspects of the optical comparator that require careful attention, but not any more than any other tool, such as a precision micrometer.
With proper use, it can be highly accurate and save a tremendous amount of time. However, proper metrology methodology must be used in order to ensure accuracy.
A classic mistake is to have the workpiece out of square with the table of the comparator. This gives an obviously false reading, yet it happens more often than you might imagine.
Injection mold makers, tool and die makers and precision machining operations all use the comparator on a daily basis. It can be used to check angles, radii, distances between centers, intersection points, thread depths, thread pitch and many more details.
Some of these details, such as thread pitch, are actually quite difficult to inspect any other way. This is especially true in the case of tiny threads, where it is impractical to physically hold wires and a micrometer to measure.
The Metrology Handbook, Second Edition