When I tested one uf the used Record Players I bought, the Feickert Adjust+ software showed quite some speed deviations. I was curious to find out more and came across a number of threads on different Internet-Forums regarding plotting the results of a Speed test as polar plot to get a better idea on how the deviation looks like and how to find out the reason of the deviation.
Here is a Collection of Links to keep together what I found out so far.
- A Blog Entry regarding the Analysis of Turntable Speed Stability 
- A Method to do Polar Plots "by Hand" 
- The Pink Fish Media Thread 
- The DIY Audio thread which is somehow the successor of the Pink Fish Media Thread 
- IQ FM Demodulation of Wow and Flutter Signal in Software 
- Python Audio Restoration Suite