I–V plot

By convention, when plotting an I-V characteristic (current vs. voltage curve):

Variable	Symbol	Axis	Variable type	Axis name
Voltage	V	horizontal (x-axis)	independent variable	abscissa
Current	I	vertical (y-axis)	dependent variable	ordinate

In this orientation the slope of the curve (m) is in Siemens, which is 1/Ohms. When plot as V-I (flipping the axes) the slope is in Ohms.