Measuring the Length of a Pipe with Standing Waves?

The purpose of this lab was to measure the length of an open pipe by swinging it around and creating standing waves.  A microphone connected to a sensor was positioned near the swinging pipe and recorded all necessary data--omega specifically.

Although it may not be distinguishable in the photograph, omega equals to 3859 rad/s for the first case. Hence for the first case f-1 roughly equals to 614 hz.

 Again it may not be distinguishable in the photograph, but for the second case, omega = 5068 rad/s.
Therefore f-2 equals 806 hz.

From here, there are three equations and three unknowns.  (eq1) f-1 = (n-1*V)/(2L)
(eq2) f-2 = (n-2*V)/(2L)               (eq3) n-2 = n-1 +1

After solving for the wanted unknown length of the pipe L, one gets .837 meters.