Buchla 259e; what exactly is the purpose for the sinewave in principal osc?

Hello, i try to understand the use case and purpose of the sinewave of the principal osc. Buchla said “applied to the wavetables”, but the documentation does not say how.

Other descriptions said, that morphing and scanning the wavetables is cv-controlled from the modulation osc, but no word about the sinewave.

Does anybody know the purpose of the sinewave?

Thank you

Karl