I'm having some trouble prooving a basic compound pendulum theory - my company makes a piece of kit designed to do just that. In a simple experiment involving a long thin bar which is set on a knife edge and allowed to swing freely I have been changing the length of the bar and measuring the time period. The equation is tau = 2 pi * sqrt((k^2 + h^2) / g * h) designed to enable us to find a local estimate for g (gravity) and k - the radius of gyration of the rod. Plotting a graph and rearranging the eqn into y = mx + c gives an estimation of 9.84 for gravity (very good) and 0.268 for k. The theory for k is simple, Rouths Rule states k^2 = (L^2) / 3. This gives k = 0.528. Help. Have redone the expt over and over with increasing accuracy to no avail. Am confident that Rouths Rule holds as is 12.7mm diameter st/st rod with L = 915mm.