Measuring key bed to string for action regulation. Technicians: please share your ideas too!

IMPORTANT: the action must be checked afterwards in the piano by playing the piano softly and making sure that it sets off properly and drops back without any bounce back onto the string. To get an accurate regulation of hammer blow distance, set-off or let-off, drop screw, spring tension, etc, it's important to get as accurate as possible measurement of the distance between the key bed and strings.