Code review comment for lp:~richardw/jarmon/independent-ds-transformers-1188220

I applied your diff and it does give properly spaced negative ticks, but I couldn't clearly understand why.
I came up with a slightly different condition which seems to have the same effect and which I think I understand.

See what you think and let me know if it works for you.

I also added a couple of extra step sizes because (on my system ) I was graphs with only two tick labels.

Thanks again for testing.

-RichardW.