1. Hang a small ball on a string. Measure length of the string and record it in the table below. Now, you have a simple pendulum.
2. Swing the pendulum back and forth. The angle between vertical axis and thread should not exceed 10 degree.
3. Record the time (t) pendulum completes N>10 oscillation. Repeat 3 times for same length for better result. The period of the pendulum is $ T = < t >/N$. Here, $ < t > = (t_1 + t_2 + t_3) / 3$ is mean value of the three measurements.
4. If you have single oscillation time record for same length of pendulum, just fill the last three column with the same value.