ORGAN TUNING: Setting the pitch and laying the first tuning scale on completely untuned pipework.

WARNING: This video is intended for anyone interested in the technicalities of tuning. For anyone else, it will be like watching paint dry. You have been warned(!)

The recording was made in the workshop as part of the restoration of a small organ which had been built, or repaired, in the 1860s, and had become unplayable.
The completed organ can by seen and heard on You Tube, by searching "Samuel Wesley - Gavotte for organ" uploaded by Culture Vannin.
The pipework having been cleaned and repaired and newly fitted with stainless steel tuning slides or newly fitted stoppers, was therefore violently out of tune.
The first step (not shown) is to set the middle C Principal pipe to a reasonable standard pitch (in this case, A440) by soldering on an extra length of metal and then trimming it to length. This pipe is not fitted with a tuning slide, as it holds the pitch for the whole organ and is not usually altered. (Fine adjustments are made with a tuning cone.
The video starts with this 'pitch pipe' corrected. The C pipes of the other stops are then tested to see if they will be tuneable at that pitch.
After that (starting at 2min. 39 secs in) the middle octave of the Principal stop has to be tuned to its middle C in such a way that the 12 notes above (C#, D, D# E, etc.) are evenly spread (musically speaking) between middle C and the C above. This style of tuning is called 'equal temperament', because the notes are equally 'tempered' (i.e. 'spread', by tuning them sharper or flatter than perfect) across the octave. With this system, there should be no 'key colour' between the different keys, though some people claim key colour still exists in equal temperament tuning. Whether this is so, merely because the person has an degree of perfect pitch, as I suspect, is not possible to determine, though it would be interesting to have someone listen to a piece in what they deem to be a 'bright' key, and then play the identical recording at a different pitch, using modern technology. If key colour exists, the piece should still be 'bright', despite the pitch change.
Notice that the tuning of this middle octave is carried out by the tuner, solely though listening to a series of intervals (fourths and fifths, musically speaking) held by his tuning assistant at the keys. Each pair is tuned either sharp or flat by it's unique amount. The tuner has to memorize the degree of out-of-tuneness for each of the 12 pairs, taking account of temperature and other factors. No electronic tuner is needed for someone who has this technique.
The intervals held by the tuner's assistant are: C-G, G-D, D-A, E-E, E-B, B-F#, C-F, F-A#, A#-D#, D#-G#, G#=C#, and (the test interval, as F# has already been tuned) C#=F#.
This first tuning is to get the notes roughly correct, and was followed by another, finer tuning.
The rest of the stop was then tuned with reference to the middle octave, and the other stops of the organ with reference to the Principal stop.