A low cost digital multimeter.

A multimeter is an electronic measuring instrument that combines several functions in one unit. The most basic instruments include an ammeter, voltmeter, and ohmmeter.

Other features available in some units:

1. A continuity tester that beeps when a circuit conducts.
2. Digital output (as a number, rather than a scale reading) of the quantity under test.
3. An amplifier to sense small voltages, currents and high resistances.
4. Measurements of inductance and capacitance. This is helpful to test components, and therefore much used by technicians that must build and repair equipment.
5. Tests of diodes and transistors. This is popular with technicians who have to fix broken equipment.
6. Scales and sockets for temperature measurement with standard thermocouples.
7. An intermediate-frequency oscillator, a detector and an audio amplifier with a speaker, to diagnose and tune radio circuits. This used to be standard on some Russian models. It is an inexpensive compact substitute for an oscilloscope. It permits one to hear a signal, rather than see it.
8. A slow oscilloscope. This is appearing in some high-end computer-controlled multimeters.
9. A telephone test set.
10. Automotive circuit tester.
11. Record high and low voltage snapshots

An analog multimeter

Multimeter for testing sensors (http://www.launch-techs.com/)