Solar Carbon Fiber Digital 6 Inch LCD Vernier Caliper Micrometer Guage Made of lightweight Non-marring carbon fiber material. Measurement in both SAE (inch) or Metric (mm) with conversion . Zero setting in any position Low Battery Warning by Flashing Displa. Can be used in Reloading, laboratory, medical office, wood shop, farm, school, and at home. It is suited for measuring jewelry, Magnetic objects and charged objects. This digital caliper With dual power system solar/battery. --When light brightness is over 200 LUX, the battery cell won't work and the solar board will supply power. --When light brightness is under 200 LUX, the solar board won't work and the battery cell will supply power.