Measurement

An ammeter measures the current flowing through a circuit. The symbol is a circle with the letter A inside. Ammeters must be connected in series with the circuit so all current passes through them.

An ohmmeter measures the resistance of a component or circuit path. The symbol is a circle with the Greek letter omega inside. The component must be disconnected from the circuit before measuring to get an accurate reading.

A voltmeter measures the potential difference (voltage) between two points. The symbol is a circle with the letter V inside. Voltmeters are connected in parallel across the component being measured.