C. H. Stoelting Dual Pendulum Reaction Timer

This apparatus allowed the time elapsing between two key-pressing responses to be measured. Pressing either of the two black buttons released the corresponding metal disk and a count of the number of swings before they became sinchronized allowed calculation of the elapsed time difference. The pendulums were set to exactly equal lengths by running the metal rod through the holes in each pendulum and adjusting the strings to equal tension. It was manufactured by C. H. Stoelting Co., Chicago, Illinois.