Galvanometer is a very sensitive instrument. Only a small current is required to cause notable deflections in the dial. A voltmeter will be added in parallel between the points across which we intend to measure the voltage drop. So the galvanometer will be directly exposed to the same voltage which is being measured. Therefore, to prevent the damage to the instrument, only a small current needs to be passed through it. This is achieved by putting a high resistance in series with the galvanometer coil.