A vernier refers to an auxiliary scale, named after Pierre Vernier, used with a main scale (like on a ruler or caliper) to achieve higher precision in measurements, allowing readings between main divisions by finding where lines align. The most common application is the vernier caliper, a precise tool for measuring internal/external dimensions and depths in engineering and machining, offering accuracy beyond simple rulers, often to 0.02mm or 0.001″. It’s also the name of an American educational technology company, Vernier Software & Technology, which produces sensors and graphing software for science education.