Review on Precision Measuring Made Easy With GemRed Digital Tool Set For Table Saw - GR905 Angle Gauge GRSET905 by Adrian Smart

Hard to determine the accuracy - when close to 90 degrees, it begins to jump by about ±0.5 degrees - fine enough for rough work, but that amount of error adds up.

Hopefully that doesn't apply to smaller angles, like 45 degrees. Otherwise, it's easy to use and is fairly responsive, and the magnetism is nice.