TITLE: Which value goes on which axis in "plot $a$ against $b$"?
QUESTION [5 upvotes]: When the question asks to plot $a$ against $b$, which value should go on which axis?

REPLY [10 votes]: In my experience, the sentence 

Plot $y$ versus $x$

means that $y$ is considered as a dependent variable, and $x$ as an independent variable. So $y$ goes on the vertical axis.