Subject: Axis for standard curves

Hi, I'm using the Lowry Method to look at protein content, which requires a 
standard curve to find out my sample's protein content. So for the standard 
curve, I wanted to use the protein concentration as the x-axis and absorbance 
for the y-axis, since the absorbance is depended on the protein concentration. 
But I was taught to use absorbance as the x-axis instead, because I will later 
use the absorbance to calculate the protein content.
Which axis should I actually use for protein concentration, and does it 
matter? Thanks!

Re: Axis for standard curves