Please note: Gas motors give the RPM of the crankshaft but other fast running shafts may influence the reading.
After using the Sirometer a few times taking RPM reading will be easy. If the top part has turned heavy after having been used for a time, put a drop of thin oil into the brass-wire-loop, after the brass-wire has been turned out.
800-50 000 rpm
14-750 cycles per second.