Mitutoyo 500-195-30 Advanced Onsite Sensor Absolute Scale Digital Caliper, 0-4" Range New electromagnetic inductive AOS sensor- Improved resistance to environmental conditions such as dirt, oil and water that can cause false readings Increased battery life - 3.5 years under normal operation ABS sensor - Eliminates the necessity of setting the reference when tool is powered on Large and clear LCD readout. The Zero/ABS key allows the display to be Zero-Set at any slider  position along the scale for incremental comparison measurements. This  switch will also allow return to the absolute (ABS) coordinate and  display of the true position from the origin point (usually jaws-closed  point).