I have a figure showing that on different datasets, method 1 is x times faster than method 2. What is a good x axis label?
There are several possibilities. The one you suggested is OKish, but I'd prefer a shorter form like

Running time ratio A/B

Another possibility is to denote by t(A) and t(B) the running times of the two data processing methods and label the axis as

t(A)/t(B)

Finally let me point out that the unit symbol for second is &quot;s&quot; not &quot;sec&quot; [SI Brochure], and that a ratio is just 6, 3.6 etc. without appending any multiplication symbol.