OK I give up, everything people suggests does not seem to work. Wording on Edexcel worksheet: "Hold a smartphone with a frequency app near the rod and note down the peak frequency" We have tried the following apps: VisualAudio Real Time Spectrum Analyser sound analyser PRO Audio Frequency Counter NONE of the above will give us a single value for PEAK FREQUENCY that we can then use to CALCULATE the speed of sound. I am fully aware that it makes more sense to measure speed and then calculate frequency but we're trying to follow the method as laid down by exam board. We have tried contacting exam board but they are less than helpful. The only app we have found that works is SAMSUNG: Frequency Counter - but relies on one pupil at least having a Samsung phone. I have a picoscope that does the job about 2 in 3 times, however software is very un-user friendly and requires my presence in the lab as it is only on my laptop and cannot be put onto any other computers. Also results are extremely variable and difficult to get 3 vaguely similar readings. SO: what I want to know, what is everyone else doing with this one please?