In practice shock resistance is generally tested by applying two shocks (one on the 9 o'clock side, and one to the crystal and perpendicular to the face). The shock is usually delivered by a hard plastic hammer mounted as a pendulum, so as to deliver a measured amount of energy, specifically, a 3 kg hammer with an impact velocity of 4.43 m/s (This will deliver approximately 30 Joules of energy to the watch). The watch must keep its accuracy to +/- 60 seconds/day as measured before the test.