Prather Pitch Gauge has been around for at least 40 years, and can still be found.

http://www.quicktechhobby.com/Airpla...r_products.htm

The prop is attached to the moveable base and placed in one of the numbered stations, while the measurement bar is raise to flush with the back side of the blade. When in position, the pitch is read from the chart. The "station" increment is metric, while the pitch is in inches.

For a whole host of reasons, making a prop that works well is not a simple thing to do, and is perhaps the most difficult subject in aerodynamics. But for most model applications, simple changes can improve performance.

I would only use one to modify wood props. One area that wood props tend to have probems with is unequal pitch from blade to blade. No modification of the prop blades is required to correct this, rather you scrape the hub on the back side to even up the pitch.