How it works
An ammeter is a measurement instrument used to measure the electric current flowing through a specific branch of a circuit. To measure current, the circuit path must be broken and the ammeter inserted in series so that all the current you want to measure flows directly through it.
An ideal ammeter has zero internal resistance, meaning it does not cause any voltage drop or restrict the flow of current. Never connect an ammeter in parallel across a power source, as its near-zero resistance will cause a dangerous short circuit!