Measure the voltage of a resistor without error

Question

We have a simple circuit given, a resistor $R_x$ and a fixed current source with $I = 50 \, \mathrm{\mu A}$. Now over the resistor there is a currentmeter which has an internal resistance. In any case some of the current will go through the currentmeter and therefore the result will be slightly off.

The question asks us to rearrange that circuit so that no measurement error is made. We can use additional parts like a power source or a resistor with variable resistance or anything else.

Is there some way to do this other than using a currentmeter with a higher internal resistance?

Answer 1

Use Wheatstone bridge:

http://en.wikipedia.org/wiki/Wheatstone_bridge

This is classical way of measuring resistivities with no error due to imperfectness of measurement instruments (e.g. galvanometer).