Simple harmonic motion-experiment

[Smileyxx]

Homework Statement

I was being asked to find the limitation and possible ways to improve the following experiment

Cantilever experiment to record the time of fixed oscillations as the length of the ruler with a fixed mass increases each time.

The Attempt at a Solution

Limitation-air resistance, weight affects the force needed to swing as the gravity is pulling down harder because of the increased length of arm.
Improvement-?

 

[Spinnor]

The description the experiment could be better, maybe a sketch included. I had to read it several times and I'm not clear what is going on.