English: Drawing of Repsold pendulum, a freeswinging reversible pendulum developed in 1869 by German instrument maker Adolf Repsold for use as a precision gravimeter in geophysical serveys. 56.0 cm long between the interchangeable knife blade suspension points, it had a period of 3/4 second. Although symmetrical in form, one of the weights on the end was lighter than the other. It was swung from one built in knife edge pivot and the period timed, then turned upside down and swung from the other pivot and timed. From the two periods and the distance between the knife blades, the gravity could be calculated. Alterations to image: none.