I have a formal lab due, and my idea is to use a bifilar pendulum, model its period using experimental data, and examine the effect of the length of the strings on the amplitude of the period. For anyone unfamiliar with it, here is a picture of the pendulum. This is how I plan on setting up my experiment: http://labs.physics.dur.ac.uk/level1/projects/images/gallery/img_5633.jpg My control variables will be the distance between the strings and the angle the rod is turned to begin the oscillation. I plan on shining a laser at the end of the rod, which will reflect the light back at different angles. If I can measure the amount of time it takes to cross a distance, I can plot a time vs displacement/degrees from equilibrium position. But I'm not sure how I can accurately measure the time. I don't have the budget for expensive gadgets. Is there any way to do this? Thanks for any help.