Discussion about the Korg PolySix synthesizer

I was tuning my Polysix, but didn't touch the D#4-E4 trimpot,
Was only using the high/low/mid trims of overall and osc sections.

However, I noticed that on some presets the synth is stiil out of 
tune. The strange is that the lower C and upper C of a certain octave 
can sound pefectly in tune, while the F# for example on the same 
ocatve is out of tune.... I wonder it has anyhting to do with the D#4-
E4 adjustment... What does it do ? does it determine the interval 
between D#4 and E4, which can stretch up and down the basic scale ?
(I guess in that case that a perfect tune of the D#4-E4 pot will 
result in a perfect C4-C5 tuning, while if not, C4 and C5 interval 
won't be perfectly an octave ?)

The procedure I followed for tuning the Polysix was

- SW1 to "normal tuning" mode
- VR2 ,3 , 15 and all 10 and 11 to mid position
- Starting to tune OSC0 using VR15, 2, 3, 10, 11 (of osc1) NOT 
touching VR14 (D#4-E4)
- Tuning OSC1 to 5 using each ones VR10 and 11
- When "tuning" I checked for every A note on each octave with a 
chromatic tuner, so it is 0 to 1 cents from the perfexct tune.
Actually excpet for the lowest A and the 2 upper A's all others are 0 
cents tuned !

So what is wrong ?

Thanks all.