$($IMPORTANT SPECIFIC INSTRUCTION FOR THIS LAB$).$ For a given length, simultaneously release $($ALWAYS from the same point$)$ the bob and start the timer. Let it oscillate three complete oscillations. Place the amount of time it took to complete these three oscillations starting in the second cell of column B $($cell B$2).$ Repeat this timing even for this length and place that value in column C$.$ Finally, in column D in cell $2,$ type $($without the quotes$),"=$AVERAGE$($B$2$:C$2)".$ So$,$ you are timing the time it takes for three oscillations twice so you can take the average of these as your final value.