Kyle Irwin asks about tuning a small 20-key barrel organ and surmises
that it is tuned to A=435 Hz.  Don't assume anything as far as pitch
and temperament are concerned.  Firstly, the scale will be written on
the keyframe, and if not, one can ascertain the scale, particularly on
a small organ, by playing each note in turn and listening to the
intervals between adjacent notes.

The organ will not be so out of tune that this cannot be done.  The
melody section may have open pipes which are 'dead length'.  This helps
a lot as long as someone hasn't got at the organ and altered these.

Tune the rest of the organ to the dead length pipes.  If all pipes are
stopped then look at the longer bass pipes, which tend to have less
adjustability and will most probably never have been touched, and
ascertain the pitch from these.  Tune the rest of the organ to these
pipes.  That covers it as far as pitch of the scale is concerned.

Next one must sort out the correct temperament.  If you don't know what
I am talking about here, just tune it to equal temperament as given by
your tuning meter.  If you understand temperament then choose one
suitable for the limited scale of the organ.  It will sound better for
it.  That's about as far as I can go without seeing the organ.  The
rest comes from experience.

Nicholas Simons, GB