Calibration and repair services are companies that calibrate and repair laboratory and scientific instruments, test and measurement equipment, and industrial sensors. They are located across North America and around the world. Calibration and repair services differ in terms of expertise. Some companies specialize in the preventative maintenance or calibration of acoustic, avionic, environmental, fiber optic, marine, medical, and geophysical instruments. Others troubleshoot and adjust displays and panel meters, electrical and electronic test equipment, industrial computers, and process instruments. Calibration and repair services that rebuild, replace, and repair analytical instruments and laboratory equipment are commonly available. Analytical instruments include shakers, environmental test chambers, laboratory ovens, mechanical test equipment, chillers, baths, and sample preparation equipment. Laboratory equipment includes spectrometers, microscopes, chromatographs, pH meters, TOC analyzers, colorimeters, titrators, diffractometers and other specialized instruments.