Hello,

  I know that this method seems funny (and Alice needled me) so I'm
looking at the various problems: Turns out that no-one ever heard of pipe
organs de-tuning themselves, that the resonant frequency is linearly
proportional with the column height (strictly linearly) and that very
small length changes give small but very constant frequency changes.
Atmospheric pressure and temperature do not play a role as far as pipe
organ experts know. So it should work even over changing temperature.

  My device was for lab use only, so I did not have a temperature problem.

Peter