null indicator[′nəl ‚in·də‚kād·ər]
a sensitive instrument for detecting the inequality of physical quantities being compared in the null method. A null indicator may be a galvanometer, electrometer, telephone, or cathode-ray tube. If necessary, the sensitivity of a null indicator can be improved by means of photoelectric, electronic, and other types of amplifiers. Automatic adjustment of the sensitivity of null indicators is widespread; it makes possible the use of maximum sensitivity near zero and sharply reduced sensitivity far from zero. In automatic balancing, a null indicator controls a balancing system.