Measuring the pressure angle of a gear
What is the pressure angle?
How to measure it
Make a flat piece of plasticine to the thickness of the depth of the teeth on the gear in question. Place it on a flat surface. Roll the gear in it in a straight line.
This will produce the equivalent of a rack which matches this gear. Use a blade to cut through the center of the rack. Since one of the characterisitics of an involute gear is that when the gear is of infinite diameter, ie a rack, the edges of the teeth form straight lines and the angle of these lines to the rack is the same as the pressure angle of thee teeth. It might be necessary to use a microscope to measure this accurately.