PaulRB:
Kind of vague! Oscillation of what? The air in the tube? The tube itself? Is the tube made of glass, copper...? What's making it oscillate? Why do you need to measure the oscillation, can't you just calculate it from the length? What precision do you need?
Oscillation of a steel tube which is oscillated by some mechanism.
I can't calculate it as it would change by changing certain parameters (which I want to test).
Precision - I can't be sure but at this stage let's say 1% error.