Arm geometry and null points

Here's another way of putting it: with a single pivot tonearm, the stylus scribes an arc. This arc will have at most two points where it intersects the straight line which corresponds to zero tracking error

The various schemes set these two points at different disc radii according to formulations which attempt to minimise either simple errors or the consequences of these errors.

Different tonearm lengths change the curvature of the arc but the position can always be adjusted so the arc has the same two intersection points..

This last statement assumes the radius of the arc is not made impracticably small.

Mark Kelly