Abstract: A biplane goniometer including a platform having a first planar surface thereon. An indicia mark on the side of the platform is disposed in plane parallel to the first planar surface. A flexible, stable arm is pivotally attached to the platform and the stable arm is disposed in a plane substantially perpendicular to the first planar surface. The stable arm has a reference line disposed longitudinally thereon. Measuring data, including calibrated numbers, is disposed on the stable arm in an arc about the axis for measuring the arc between the indicia mark on the platform and the reference line on the stable arm.