You know you've been using zero-based indices too long when...

I was reading about population genetics of unusual sex ratios and encountered this bit:

Then the fitness of the second organism is proportional to:

x /( x + x₀ ) [ ( 1 - x ) + ( 1 - x₀ ) ] + ( 1 - x )

Where x is the sex ratio produced by organism #2 and x₀ is the sex ratio of organism #1.

Confused by the variable names, I mentally corrected x to x₁:

Where x₁ is the sex ratio produced by organism #2 and x₀ is the sex ratio of organism #1.

One for the second organism and zero for the first? This seemed perfectly intuitive and unconfusing to me, because it's so familiar. Only when I tried to put it into words did I see the problem. Numbering from zero breaks the correspondence of cardinal to ordinal numbers, so speaking of it means fighting natural language with every word. It may be mathematically natural, and sometimes more convenient (and sometimes less), but I still prefer one-based indexing.