Parallel

The voltmeter must be in parallel across the test component because it compares the potential at the component's two ends. A switch allows the circuit to be disconnected between readings.

The voltmeter therefore forms a separate branch in parallel with the component.

In a parallel circuit, each resistor provides a separate path between the same two points. Adding a second resistor as a new branch gives charge another route through the circuit; it does not force all the charge through an extra resistor. Each branch has the supply potential difference across it, and the branch currents combine at the junction.