Hi,
Like most of VCO you must turn the frequency knob at noon. Big frequency knob on VCO are used to change the range of octave (and tunning) (well on plaits you can change the range in other way (see manual) (so the big frequency knob is kind of a fine tuner).
To be always on the perfect tune, you have to wait that the module warm up, or use this king of module : https://www.modulargrid.net/e/bastl-instruments-1983
Cheers
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