How To Test Gem Turn on the switch. Make sure only 1 light is lighting up on the scale. Wait few seconds for the probe to heat up until Lamp on ready OK. Turn on the lights numbers corresponding to the indoor temperature and diamond weight. If don't know. Set 4 lights is lighting up on the scale. Start test diamond, no need to adjust the switch switch. Use the diamond discriminator probe to make 90-degree contact with the measured object, and observe the indicator light change. It needs a little bit of force to stop it on the diamond surface and make full contact. If unsuccessful, please repeat the second step.