Calibration of ETDs

[Robert Scott]

Kevin E. Ramsey wrote:

>    When I first got my SAT, I calibrated my forks to be at exactly 440 when
>at body temperature. I achieve this by tucking it between by belt and my
>body for about two minutes. I still have one of those forks in a drawer in
>my dresser, as a back-up. I check it once in a blue moon. It hasn't changed
>by a tenth of a cent in eight years, according to my SAT, so I kinda get the
>impression that the SAT isn't changing either.

Yes, as long as your fork is not dented or bent and is kept clean and
used a the same temperature, it will be quite good as a standard.  
Some tests that I performed recently on a medium-grade fork showed 
that it takes 7.5 degrees Fahrenheit temperature change to make the 
fork change 1 cent.  So if you want .1 cent accuracy in a fork you 
would need .75 degree temperature control.

>    I was under the impression that the SAT uses a quartz crystal, which can
>only oscillate at one frequency. Let me know if you think I'm wrong.

A quartz crystal ocsillator can change its frequency with changes
in temperature, battery voltage, etc., although it does not change 
nearly as much as a fork.  And I am sure that the SAT incorporates 
all the best voltage regulation and temperature compensation techniques
to achieve stability.  But things can go wrong, so it's good to be able
to do a check-up once in a while.

-Robert Scott
 Ypsilanti, Michigan