String coupling.

[Roger Jolly]

Hi Ron,
             Checking the coupling effect in the same manner as you
described, I had similar results.
However, If you tune each string separately for full blush on RCT. and redo
them a second or third time so that each string gives a perfectly stable
reading, them measure the unison it's very consistent 0.2 to 0.4 cent pitch
drop in the killer octave range. 
I did this test in front of another tech on the list that has observed the
same consistent results.
A while back I posted some observations in tuning a full octave in the 5/6
range. These test were done on newly strung pianos and well maintained
concert grands.
I would be interested in your observations using the same measurement
technique.
Regards Roger
Roger Jolly
Saskatoon, Canada.
306-665-0213
Fax 652-0505