other points include using - small angle for pendulum (ie less than or about 5 degrees, not 45 like some one wrote in our trial and lost marks)
- having a light, inelastic string
- using as long of a pendulum as possible (we done it of the rail of the sencond level and dropped it over the side)
- not allowing external forces to interact (ie if doing it out side make sure theres no wind)
- taking the average of 10 swings to find the period (because of the small time it takes for one swing)
then using the equation T = 2pi . squareroot(l/g)
l = length of pendulum
T = period and
g = gravity