This should be doable with a calculated field. If you attach an example workbook, it'll be easier to assess your problem and suggest a solution.
Your graph should auto-arrange the axis. But like Sho said, it would be great if you can share the workbook/screenshot of it.
Thanks both for the response (have been away hence my slow comeback). Attached is a screen shot - I'll have to see if/how I can upload an appropriate workbook (the source data is from a MySQL db, and I'm very new to Tableau ...). As you can see, when a service starts up, the increase is show as millions of a percent - this first value I want to ignore.
You could resolve this using Z-Scores, and filtering out Highly significant positive Z-Scores.
You can do this via Table Calculations or LoDs (Level of Detail)
I wrote up a doc on how to do this with LoDs, but there is a link in there for the Table Calc version as well.
Let me know if you need help with it.
Thanks again for this Rody – inspired by what you’ve shown me I was able to use an even simpler calculation based on WINDOW_MAX and WINDOW_MIN (range -1 to 0) to spot a big change and exclude it.