Grandfather clocks calculating error?

Grandfather clocks are designed to use a pendulum to keep accurate time. The period of a grandfather clock is given by the formula T=2pi*sqrt(L/g), where L is the Length of the pendulum in feet, g=32*(ft/s^2) is the acceleration due to gravity, and T is the time for one complete period in seconds. If the length of the pendulum is measured to be 3ft long with an error of + or - 0.003ft, use differentials to approximate the calculated error in the period, T. What is the relative error for this problem?