Thanks for the quick reply Don!
That was my initial thought so I double checked the position of both the pitch wheel and the master tune knob, and both were centred.
My Polysix is an old model with the KLM-366A daughter board. There is no VR15, and I'm lead to believe the VR1 on the daughter board is the equivalent. However, slight adjustments to that throw the scaling way out.
Is there another trimmer on the old models that adjusts the master tune?
Thanks!