We have revised our famous „Universal Protractor“. Besides making handling easier we have enhanced the functionality as well as accuracy. On this Protractor you can find all three well known, major geometries aka Baerwald, Lofgren and Stevenson.
The general geometrical correlation of a tonearm based on a fixed pivot point are well known since the fundamental publications of Baerwald and Lofgren back in the first half of the 20th century. The conclusion of both papers was that such a tracking device must have an angular offset (zenith) with a defined overhang. The offset and the overhang vary with the effective length of the tonearm itself. While tracking the record the stylus matches tangential position in the groove at two points – the inner and outer Null points (linear tracking position). In the early 1960s another mathematician has calculated a new set of parameters taking into account that on records with classical music very often crescendos occur towards the innermost grooves (Stevenson).