Measuring the speed-of-sound, and canceling its propagatory effect on sound waves. Here we see a coordinate frame of reference as if traveling at the speed of sound to, in effect, make sound waves sit still:

Freq = 10.05kCPS (10050 CPS)

Total run length was 0 to 15 inches. (Knob protrudes, but actual distance is
right at base close to 0 and 15.)

15 inches total travel, 11 cycles.

15 inches * 10050 cycles per second / 11 cyles = 13704.5454... inches per second

= 348.09 ... meters per second.

Speed of sound at 20deg. C is about 343.2 metres per second,
but our lab was about 25deg. C,
so speed of sound would be about 343.2 +.606 m/s/deg *5 difference=

346.23m/s

so we have about 1/2 a percent measurement error.

I also tried 13631.0751 CPS, which would be 1 inch per cycle at 25deg. C., but some microphones, including this one don't work as well at that high a frequency.