Simple? Mathematical formula for two pots connected in series and parallel

Hi there, this is the first time I have posted on this forum, I have what would appear to be a simple task - I'm trying to work out a formula to represent the relationship between the two pots in this circuit:

**broken link removed**

It is actually the pitch control circuit in a Technics 1210 turntable and I'm trying to work out how it works as an educational exercise. I have tried various combinations of series / parallel sums but can't seem to get the correct formula to calculate the total resistance at points A and B, given each pot setting.

Sorry for posting what is probably really basic but I'm trying to understand the calibration technique.

Thank you

Linear or Logarithmic?

Hi Mike, they're both linear...

There is something wrong with your diagram. The lower pot is totally shorted by the upper wiper to B connection.

Missing a ground?

erm, the diagram is correct I think I took it from this, the service manual for the deck. However I've done some more measurments and I think VR303 is either log or special purpose I'm not sure I think I'll look it up.... no wonder I'm confused!

**broken link removed**

The value for the lower pot wont make any change for what you measure between A and B with your ohm meter.

So it's just a waste of pots.

[edit]
Your latest post I didn't see. I was talking abourt your first post, to not making confusion.

The way I see it, in your first drawing, the 50K setting is in parallel with the B portion of the 20K, but floating and the a to b value is the a portion of the 20K, but in the schematic, you missed the ground as suggested by Mike.