The Prestige Series II Diamond Tester with state-of-the-art technology assuring quick, accurate readings to determine if a stone is real diamond or a fake. Features include: Automatic and manual mode Linear display for increased information Adjustable gain for small stone sizes Compensation for ambient temperature Fast warm-up time - 10 seconds! Portable with one 9-volt battery (included) Auto shut-off with a push button switch Unique new anti-fade circuit which compensates for stone heating Low battery indicator for accurate readings Multi-purpose alarm (a. Beeps when ready, b. Metal alert, c. Beeps repeatedly when testing a diamond.)