Bergeon 5402 Waterproof Tester Bergeon 5402 waterproof tester is for watches with 2 piece stems (split stems). Specially designed air pressure apparatus to test water tightness of watches with two piece stems, without the penetration of water. Procedure is simple. Remove the crown and mount it on the metal pipe on the pump nozzle, then place the watch on the fan-shaped support, engaging the case tube into the nylon pump nozzle. Pull the piston as far as it will go and then release. If the piston moves back towards the pump, then the watch is leaking, if the piston remains still, place the watch in the water and observe. If no air bubbles appear, then the watch is considered waterproof.