Abstract: In a pumping well, oil is normally lifted to the surface by a rod which extends from the surface to a downhole pump. A transducer is attached to the rod at the surface to sense the deformation, i.e., the change in diameter or circumference of the rod to determine change in rod loading. The transducer includes strain gauges which produce output signals proportional to the change in the diameter or circumference of the rod which occurs due to changes in load on the rod. The transducer may also include an accelerometer. The change in load on the polished rod over a pump cycle is used in conjunction with data produced by the accelerometer to calculate a downhole card. The downhole card showing change in pump load is adjusted to reflect absolute rod load by determining an appropriate offset. Various ways to determine the offset are available.