Is it ensure, insure, or assure?
dynamometer dy·na·mom·e·ter (dī'nə-mŏm'ĭ-tər)
An instrument for measuring the degree of muscular power. Also called ergometer.
device for measuring mechanical force, or power, transmitted by a rotating shaft. Since power is the product of torque (turning force) and angular speed, all power-measuring dynamometers are essentially torque-measuring devices; the shaft speed is measured separately