Vintage DD turntables. Are we living dangerously?

If Dover and Richard (and Fleib) were to refrain from commenting, we would all be the poorer for it, and this fun thread might be dead. Carry on, gentlemen.

For those belt-drive turntable owners who are concerned at the 'servo-control' jagged spikes on their Feikert Frequency Chart, here is a what Marcus Ribi from Feikert Platterspeed has to say about the change in the software....

The approximate sine wave form of the chart is resulting from eccentricity of the record. A normal measurement of WOW and flutter with a perfectly centered record will NOT show such a wave form, but a more random spiky form instead. That's what the spikes are coming from: it's a superposition of eccentricity and "real" WOW and flutter. Measurement of WOW and flutter then tries to best filter away the regular changes comig from record eccentricity to provide best results.

I wonder how accurate this is. The waveform peaks at +16Hz and bottoms at -20Hz. That's a spread of 36Hz, a little more than 1%.
A scope or a meter with a frequency counter could be used to check results.

Another fly in the ointment - Werner Ogries EE, has reported calibration errors in both HFN and Analog Productions test records. Not sure of all the gory details.

Taking a break from applied technology, how about remedial physics?
What do MPH and RPM have in common?
Time is a dimension we have divided precisely, based upon, but not dependent upon, the movement of Earth around the Sun. Our division of time does not exactly agree with the rotation of Earth and has to be corrected at regular intervals. It could be divided arbitrarily, but the days and seasons might not agree with nature.

The Earth rotates in a counterclockwise (west to east) direction at approx. 1040 MPH at the equator. If you went to Brazil near the equator and drove a car 100 MPH west, you'd actually be going backwards at 940 MPH and wind up in the Atlantic ocean?

Rotational speed of an object on Earth is not dependent on the rotation of the planet. Either is land speed. As long as we have precise and agreed upon divisions of time and distance, the rotation of Earth could cease and we would still be able to apply our divisions of time. We would still be able to play a football game, do the dishes and take a walk, weather permitting.

Fleib.

The error resulting from record eccentricity is surprising.

Take a small 0.5mm eccentricity on a 100mm radius and we get around a 1% error. (The tracking radius makes a difference)

Nakamichi were on to something way back then.