A simple ohmmeter can be made of 2 constant resistors, 1 variable resistor, a voltage source, and a galvanometer, or a voltmeter. One puts the unknown resistance to x, and adjusts the variable resistor 2 so that the current through the galvanometer is 0 or the voltage between the terminals of the Wheatstone bridge. As soon as 0 is obtained, find the unknown resistance:
If the terminals where the x is supposed to be are opened, the ammeter's readings are
If you should record the value of and calculate the unknown resistance according to the first equation.
If there is a voltmeter instead of G, its readings would be
If you should record the value of and calculate the unknown resistance.
Any other readings of mean that the Wheatstone's bridge is unbalanced, and the terminals of are closed.