Beats me how you guys can argue over such a simple and obvious bit of physics.
Ledermann's explanation is correct.
He mentions using the unmodulated run-out area of the record to observe scating activity.
This is better done with an entire unmodulated side of a record. These are often present on MFSL 45rpm reissues. Drop the stylus at various positions on the revolving record surface and observe how strongly and quickly the skating force pulls the arm towards the centre. Then add anti-skating and re-test. Adjust the anti-skating force until the best result is obtained in maintaining the arm most nearly stationary at different points and you will have the best amount of anti-skating to equalise the forces on each side of the groove.
Ledermann mentioned in passing that parallel tracking arms are complex and expensive and kind of excluded them on that basis. I agree that many don't work very reliabily and are difficult to set up and maintain settings. My Simon Yorke Aeroarm (an extremely rare piece I am fortunate to have, thank you Simon) works very well and cost one-quarter or less of the price of the top pivoted arms that are now $50,000 and more. I know which I'd rather have.
I use the unmodulated side to set the lateral levelling of my plinth on the fly using a fine screw adjustment, so that the arm remains stationary on a revolving record. Lateral levelling is critical for parallel trackers and this method is waaayyy more accurate than using a spirit level.
Ledermann's explanation is correct.
He mentions using the unmodulated run-out area of the record to observe scating activity.
This is better done with an entire unmodulated side of a record. These are often present on MFSL 45rpm reissues. Drop the stylus at various positions on the revolving record surface and observe how strongly and quickly the skating force pulls the arm towards the centre. Then add anti-skating and re-test. Adjust the anti-skating force until the best result is obtained in maintaining the arm most nearly stationary at different points and you will have the best amount of anti-skating to equalise the forces on each side of the groove.
Ledermann mentioned in passing that parallel tracking arms are complex and expensive and kind of excluded them on that basis. I agree that many don't work very reliabily and are difficult to set up and maintain settings. My Simon Yorke Aeroarm (an extremely rare piece I am fortunate to have, thank you Simon) works very well and cost one-quarter or less of the price of the top pivoted arms that are now $50,000 and more. I know which I'd rather have.
I use the unmodulated side to set the lateral levelling of my plinth on the fly using a fine screw adjustment, so that the arm remains stationary on a revolving record. Lateral levelling is critical for parallel trackers and this method is waaayyy more accurate than using a spirit level.