| Instrument | Use |
| Sextant | Used by navigators to find the latitude of a place by measuring the elevation above the horizon of the sun or another star; also used to measure the height of very distant objects |
| Spectroscope | To observe or record spectra |
| Spectrometer | Spectroscope equipped with calibrated scale to measure the position of spectral lines (Measurement of refractive indices) |
| Spherometer | Measures curvature of spherical objects |
| Sphygmometer | Measures blood pressure |
| Stereoscope | To view two-dimensional pictures |
| Stethoscope | Used by doctors to hear and analyze heart and lung sounds |
| Stroboscope | To view rapidly moving objects |
| Tachometer | To determine speed, especially the rotational speed of a shaft (used in aeroplanes and motor-boats) |
| Galvanometer | Measures the strength of direct current |
| Telemeter | Records physical happenings at a distant place |
| Teleprinter | Receives and sends typed messages from one place to another |
| Telescope | To view distant objects in space |
| Thermometer | Measures Temperature |
| Thermostat | Regulates temperature at a particular point |
| Tonometer | To measure the pitch of a sound |
| Transponder | To receive a signal and transmit a reply immediately |
| Udometer | Rain gauge |
| Ultrasonoscope | To measure and use ultrasonic sound (beyond hearing); use to make a Ecogram to detect brain tumours, heart defects and abnormal growth |
| Venturimeter | To measure the rate of flow of liquids |
| Vernier | Measures small sub-division of scale |
| Viscometer | Measures the viscosity of liquid |
| Voltmeter | To measure electric potential difference between two points |
| Wattmeter | To measure the power of an electric circuit |
| Wavemeter | To measure the wavelength of a radiowave |