The micrometer is widely used for measuring of industrial accessories, handicraft, pearls and jewels. It can measure inside, outside, depth and step size with two sets of and the probe. I believe that will be a good idea, if you could give your children a handmade necklace as birthday gift, which is made of pearls in oysters. The micrometer caliper will help you , it is a good partner of pearl drill. Features - ColorSilver - Material: Plastic fiber composites - Size: 23.5 x 7.5 x 1cm / 9.3 x 3 x 0.4inch(LxWxH) - Functions: Outside measuring, inside measuring, step measuring and depth measuring - Range: 0~150mm/6" - Accuracy: ±0.2mm/±0.01" - Resolution: 0.1mm/0.01" - Repeatability: 0.1mm/0.01" - Maximum measuring speed: 1.5mm/sec, 60"/sec - Operating temperature: 0~+40C - Storage temperature: -20~+70C - Influence of humidity: within 0 to 80% of relative humidity - Due to air shipping control, battery can not shipping together with caliper (Battery not included) - Large and Clear LCD Display. - Dual Solar and Battery Powered system. - Fiber Composite. - Switchable between mm and inch. - function to measurement in any position. - Depth Measuring . Inside, Step and Outside Measuring faces. - 2 Power: When the light brightness is over 200 LUX, the solar board will supply power. When the light brightness is below 200 LUX, the 3V battery will supply power automatically. Package list: 1 x 150mm 6 Inch Solar Gauge Meter Widescreen Caliper Fiber Composite Micrometer Measuring Tools