I've a standard time chart, counting up HTTP error codes. It's all fine, however I'd like to separate out the error-type codes. A good visual way would be to somehow alter them with a negative modifier.
For example I have the HTTP OK code as coming up as a total of 200 events on Monday, while I have 10 404 errors. I'd like someway to alter the 10 to -10 so that when it's graphed it's easy to identify the errors - as they all lie below the X axis. I don't need an exact answer, just a nudge in the right direction.