A shunt type ohmmeter is shown in the figure below. With

A shunt type ohmmeter is shown in the figure below. With R_x disconnected, the meter reads full scale. S represents the meter current as a fraction of full scale current with R_x connected such that
S = R_x
R_xR_p

The value of R_p is given by

I_ƒs =	E
	R₁ + R_m

With R_x connected,

I_m =	R_x	E
I_m =	R₁ + R_x	R₁ + (R_mR_x)/(R_m + R_x)

=	R_{2 + R₃}	=	ER_x
	(R₁ + R_x)		R_x + (R₁R_m)/(R₁ + R_m)

= I_ƒs	R_x
	R_m + R_p

where, R_p =	R₁R_m
	(R₁ + R_m)

S =	R_x
	R_xR_p

R₁R_x
(R₁R_m)

R₁R_m
(R₁R_m)