1. Battery Installation – Open the battery compartment door located on the side of the Pro-M by grasping the textured area with your thumb and sliding the door off. Insert “AAA” alkaline batteries into the battery compartment as indicated with the direction of positive (+) and negative (-) polarity correctly positioned in the battery holder. Replace the battery compartment door. Turn on the power switch located on the end of the tester to (ON). The warm-up time is approximately 30 seconds and after that time the tester may begin testing.

2. Prior to Using the Pro-M – First it is necessary to use the Gemoro Pro-M or other reliable thermal conductivity diamond tester, to test the stone in question for the thermal conductivity property since only Diamond and Moissanite (and no other known or common diamond simulants) share this unique characteristic. By performing this test, if the stone tests as a diamond, you will know that the gemstone should be either diamond or moissanite. You will have effectively determined that the stone in question is not one of the other known diamond simulants. After narrowing down the potential identity of the stone in question to being either diamond or moissanite, you may then proceed with performing the electrical conductivity test with the Pro-M.

3. Removal of the cap that protects the tip – Prior to using the Pro-M, be certain to remove the cone shaped cap at the end of the tester, which serves to protect the probe tip from accidentally being bent or broken. The cap may be taken off by simply applying a minimal amount of pressure as you hold it between your thumb and forefinger and gently pulling it off with a slight twisting motion. Always replace the cap when not testing.

4. Proper Procedure for holding the Pro-M– Be certain that as you develop your own comfortable technique for holding the tester that one or more of your fingers makes a contact with the metal grip area at all times for confirmation. If held in the right hand it is suggested that the tester be held (opposite hand if you are left-handed) while resting on the users middle finger on the “V” shaped bottom part of the metal plate with the users thumb and forefinger grasping the sides of the Pro-M on the metal grip area for handling purposes and to maintain control.

5. Testing Mounted Stones – Turn the switch at the end of the tester to the “ON” position and the Pro-M is READY immediately. Make sure the stone to be tested is clean and dry. With one hand hold the mounted stone and in the other hand hold the tester. Quickly yet firmly make contact with the probe tip to the table of the stone while being certain not to touch the setting. Make contact long enough to establish a reading. (One or two seconds). Always be certain not to touch the metal setting since metal (including gold, platinum, etc.) is also electrically conductive it will react to the metal setting as it would when touching Moissanite.

  • WARNING: While typically being an electrically conductive gemstone, not all Moissanite gemstones are equally conductive and in rare cases, some Moissanite gemstones are not electrically conductive at all. While the Pro-M can easily help to identify Moissanite in the majority of cases, it may be necessary to touch the probe tip to different locations on the stone by simply dragging the probe tip from the table of the stone, to the girdle, around the crown, etc. since there may be only some areas of the stone where the electrical conductivity property may be present.

6. Testing Loose Stones – Place the loose stone in a supplied aluminum testing plate or metal tweezers (the loose stone must be held by metal material) and hold it steady with one hand. With the other hand while holding the Pro-M after it has warmed up and shows its ready to test, touch the probe tip to the loose stone on the table of the stone in it center whole being certain not to touch the aluminum testing plate. Follow the normal procedure.


  • The Pro-M is a very sensitive instrument. You should always protect it when it is not in use.
  • Always replace the protective cap to keep the probe tip from becoming damaged.
  • Always recharge the NiMH rechargeable batteries so that the Pro-M will be fully charged and ready to test when portability is needed.
  • Always replace alkaline batteries after long periods of time to prevent premature corrosion or battery leakage, which is common with old or spent alkaline batteries after a period of time, because damage to the Pro-M may occur and void the warranty.
  • The probe tip must be cleaned periodically to ensure proper contact with the stone being tested. To clean the tip, take a piece of uncoated white printer paper or copy paper and place the probe tip of the tester at a 90º degree angle against the paper while gently rubbing it in a back and forth motion a few times. Repeat this process prior to testing each time to ensure the cleanliness of the probe tip.





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