Facts for Kids

A long time ago a British engineer named Donald Macadie wanted to stop carrying three heavy tools for work. He helped create the first combined tool, the Avometer, in 1923 so he could measure amps, volts, and ohms all in one small box. This made fixing radios, lamps, and machines much easier for people who travelled to repair things.

Later, companies made new versions. The first digital-style meters appeared in the 1950s, and in the 1970s someone made a small handheld digital unit that technicians could use in the field. Tools keep getting smaller and smarter.

multimeter is a small tool you can hold that helps you check things that use electricity. It can measure voltage (how strong the electric push is), current (how many tiny particles called electrons flow), and resistance (how hard it is for electricity to pass). You might use one to see if a battery is good, if a light will turn on, or to check a toy's wires.

Some multimeters are analog and show a moving needle, and some are digital and show numbers. Digital ones usually give easier-to-read answers. Which kind would you try first?

A multimeter usually has a display, a dial or buttons to pick what you want to measure, and two or three wires with tips called probes. Probes can be pointy for small contacts, have clips like crocodile clamps to grab wires, or be tweezers for tiny parts. Portable meters use shrouded banana jacks where the probes plug in so the metal is covered for safety.

Inside a digital meter are little electronic parts that turn the electrical signal into a number on the screen. Bigger bench meters have more parts for higher accuracy, and special meters can connect to computers or show small moving graphs.

Always use a multimeter with care. Check that the leads and insulation are not cracked, and plug probes into the correct holes for what you measure. Never touch metal tips while testing a live socket or a car part that is powered; ask an adult for help. Use the right range on the dial so the meter does not get damaged.

For some jobs there are safer alternatives: a clamp meter can measure big currents by clamping around a wire without touching it, and a non-contact voltage tester can tell you if a wire is live just by holding it near the wire. Which tool would keep you safest for checking a battery?

Most multimeters check three basic things: voltage (both DC which flows one way, and AC which swings back and forth), current (how much electricity flows), and resistance (how hard it is for electricity to pass). Many also test continuity — a quick check that makes a beep when two points connect — and they can test diodes or batteries.

Some meters add extra functions like measuring temperature, sound frequency, or capacitance (how much charge a part can hold). These extras help when you are fixing different things, like a radio or a kitchen gadget.

A digital meter reads the electrical quantity many times and shows a number; an analog meter moves a needle smoothly. Digital meters are usually more accurate and can show tiny changes as more digits. But every meter has limits. One important idea is input impedance — it tells how much the meter tries to take from the circuit. A high input impedance means the meter will not change the thing you are testing.

Another limit is called burden voltage when you measure current: the meter puts a small resistance in the circuit and that can drop voltage. So choose the right range and tool for the job.