Precision measurement. A technician using a pair of digital calipers. These ae similar to the more familiar vernier calipers, but have a digital readout. In the background is a digital micrometer mounted in a clamp. Both are far easier to read than traditional instruments which rely on vernier scales, and give more repeatable readings. The technician is here measuring the dimensions of glass pentaprisms - five-sided prisms found in single-lens reflex cameras and some designs of microscope.