For a simple pendulum practice with clamp, boss head and resort stand assembled, also a string attached to the end of clamp and a bob, then swings it and measure the time for it to complete a period. At the end use the information collected to calculate acceleration due to the gravity by the formula g = 4π2l/T2. What could the accuracy and reliability be effected? (Equipments, angles or the error should avoid) And what kind of string or bob will most suit? Why?