The Windchest In Pipe Organs - Viscount Cantorum Duo Plus Reference Manual

Appendix
Barca
The Barca temperament is based on six fifths (from C)
reduced by 1/6 of syntonic comma each, and one fifth (on
Eb) reduced of the remaining skisma. Therefore there are
no Pythagorean thirds, and tonalities with many alterations
still sound well.
Neidhardt II
It consists of three pure fifths on E, Ab and F; three reduced
by 1/6 of a Pythagorean comma on C, G and D; the
remaining six on A, B, F#, C#, Eb and Bb, reduced by 1/12
of a Pythagorean comma. It shares the exact intonation of
six keys with Vallotti's Temperament: C, G, D, A, Eb and
Ab. The other six are shifted slightly in favor of better
euphony in the case of many accidentals. It is therefore a
circulating temperament that allows you to play in all keys.

The windchest in pipe organs

The windchest is a crate where the air from a bellows (manual or electric) is spread equally among the pipes.
Usually, each manual has its own wind chest. However, there are different kinds of wind chests: some contain
only one stop, while other have an additional crate filled with air from the bellows that spreads air to all the stops
for each note.
Here you will find a short description of each kind of wind chest simulated by the organ.
Single cusp
The tallest, broadest pipes are located in the centre. As the pitch rises the pipes are
gradually distributed further and further to the outside, alternating (e.g. C to the right, C#
left).
Double cusp
There are two separate cusps, both resembling to the single cusp described above. The
lowest keys sound in an intermediate position, between the centre and the outside,
alternating (one on the right cusp, one on the left cusp). As the pitch rises, rises the pipes
are gradually distributed further and further to the outside, alternating (e.g. C right, C# left).
EN - 50
Reference Manual