Ondioline tuning notes:
There are two prominent knobs just below the keyboard on the front of the Ondioline. The right knob is the Accord General, or overall pitch control. The left knob is the octave selector.
The grommets in the middle (CV-1, CV-2, CV-3, CV-4) are the variable caps and are for tuning each octave relative to the other octaves.
The pots to the right of the Pitch Control are RV1, RV2, and RV3 and are for temperament adjustments on each octave — that is for tuning each octave such that the keyboard is in tune with itself over the range of a given octave. RV4 is on the underside of the keyboard assembly on the back. It tunes Octave 4 (the highest octave.)
To tune the Ondioline, turn it on and let it warm up at least 15 minutes.
Set up a frequency counter on the speaker output. Select Octave 4, the highest octave. Select switches C and E on the front switch array.
Put the overall Pitch control in the center of its travel, such that low A on the keyboard is near A-440 hz. Play the highest A on the keyboard - 1760 hz - and adjust RV 4 on the underside back for 1760 hz.
Play low A, adjust CV4 for A 440. If you run out of range, adjust the overall pitch control (Accord General.) This has to be done back and forth a number of times, as RV4 changes the width of the oscillator, changing the high frequency faster than the low, but affects the whole range nonetheless.
Play high A, adjust RV4 for 1760 hz, play the low A, tune CV4 for 440 hz, go back to the high A, adjust RV4 for 1760, and so on. It is absolutely crucial that this adjustment be made first and accurately, as all the remaining adjustments develop from it.
Next select Octave 3. Don't touch the overall Pitch control!! Play low A, adjust CV3 for 220 hz, play high A and adjust RV3 for 880 hz, back and forth. Check Octave 4 occasionally to make sure it hasn't drifted.
Select Octave 2. Play low A and tune CV2 for 110 hz, play high A and tune RV2 for 440 hz, back and forth.
Select Octave 1. Play low A and tune CV1 for 55 hz. Play high A and tune RV1 for 220 hz, back and forth.
Select Octave 4 and test for drift. Note that any changes made in the upper octave tunings change the tunings of the octaves below. Note that the overall pitch control will change the whole scale, all octaves. Note that use of metal adjustment tools changes the pitch, so use plastic screwdrivers. Touching any metal part with your hand will slightly change the oscillator frequency as well.
The oscillator circuitry in the Ondioline is not the most stable thing. Louder volumes cause a corresponding B+ drop, which in turn changes the oscillation frequency slightly. But it's all part of the Ondioline charm.
"How to Tune" section of the Ondioline manual
HOW TO TUNE YOUR ONDIOLINE
On the front panel, along the keyboard of Ondioline, 5 knobs appear; on the left is the transposing knob (arrow shaped),also called the octave (register) switch; on the right are the 4 tuning knobs (with milled sides), for matching the tuning to a piano or orchestra.
When you turn a tuning knob clockwise, the pitch goes flat, and vice-versa (the opposite direction to what you would expect). The total range is fairly wide (about a tone and half) allowing you to tune the Ondioline to another instrument that is very sharp or flat.
Each register set by the octave switch is tuned by means of it's corresponding milled knob. Start by tuning Register 4 (using the far-right of the four tuning knobs), then tune Registers 3, 2, and 1. DO NOT switch back to a higher register before tuning all the lower registers. Tuning a high register can slightly affect the lower registers - so this order must be used! N.B.: Transporting the Ondioline can slightly affect tuning, so always check it after moving the instrument.
[Note - When using the "grommets" to adjust temperament I think it is recommended to play the second A or G from the bottom of the keyboard, use the tuning knob to set it to the correct pitch, THEN use the corresponding grommet to adjust the higher and lower octaves in the same register. I kind of figured this out from the extremely technical manual you sent me.]
The left knob (octave switch) makes it possible to switch instantly to high or low registers. By this means, although the Ondioline keyboard spans three octaves, (G to G) the actual range of the instrument is six octaves. Thus the octave key has four positions. These are not marked, for aesthetic reasons, but the positions go from the far left (lowest pitch - called Register 1 in the timbre list) to the far right (highest pitch - Register 4).
N.B.: For reference, in Register 3 the bottom G of the Ondioline corresponds to the lowest note of a violin.