The equation of simple pendulum
Taking logarithm on both sides
Now for calculation of maximum error of g every error term should be taken positive.
Hence equation (1) becomes
In percent form it becomes
Now it is given that in measuring
Again the resolution of watch used for the measurement of T being 1s (the smallest graduation on the face of the watch),error for the measurement of time for 100 oscillations will be 1s i.e.
Now time measured for 100 oscillations is 90s. So time period
Now the percent error in measurement of g by equation(2)