In the hammer, we have simple accelerometer sensor. The signal that we get from an accelerometer has several components:

- projection of gravitational acceleration on axis of the accelerometer. (Should be close to zero when hammer head is in horizontal plane)

- acceleration of hammer head driven by hand of experimentator before and after impact

- strong acceleration, or better said deceleration at the moment of the impact (this one is proportional to force of impact)

- acceleration of sensor due to vibration of the hammer and it's parts (mainly as a consequence of impact)