Page "Ohmmeter" Paragraph 2

The original design of an ohmmeter provided a small battery to apply a voltage to a resistance.

It uses a galvanometer to measure the electric current through the resistance.

The scale of the galvanometer was marked in ohms, because the fixed voltage from the battery assured that as resistance is decreased, the current through the meter would increase.

Ohmmeters form circuits by themselves, therefore they cannot be used within an assembled circuit.