Frequency accuracy?

[Newton Hunt]

Most likely the easiest is to use a Sanderson Accu-Tuner when you can
access one.  It's  A440 is accurate to 0.05 cents or better.  

Your fork is likely off, not matter how big it is.  Check the
temperature against the side of your neck which is most thermally
sensitive and most easily reproduced.  You want it to be cool, not
cold, against your neck. You should check the temperature of the fork
every time you tune.  Compare the fork to the SAT the file the ends of
the tines if it is flat (most likely) the place the fork on a piano
plate or heavy steel plate to cool down and repeat the process until
the temperature of the fork and the SAT agree with each other.  You
fork is tune.

If the fork is sharp then file at the inside base of the tines.

You could likely do this over the phone if need be.

THere is an A440 tone available from the bureau of Standards but I
don't know where to access it.

At a Texas State COnvention I set up a booth and tuned folks forks for
free.  Out of 15 or so I did NONE were right on although some required
but a mere touch of the file.  I also had a grinder for making radical
changes.

As for the "machines" they depend upon a crystal for their pitch
standard.  So does the SAT for that matter but the one in the SAT is
HUGH.  Shocked a electronics tech friend of mine when he saw it.  The
smaller the crystal the more it will drift and the more often it will
require calibration.  They should be tune with an SAT as well but will
need checking more often than a fork.

		Newton