[garyc8]

A good discussion of this is available in Mason's "Gambling Theory and other topics.
I would recommend separating your results by limit. For example, on my spreadsheet I have one sheet for 5/10 hold'em, one for 10/20 hold'em, etc.
You compute your overall SD by dividing the SD by the square root of the # of hours played. Figure your real long term expectation is within 3 deviations of your results.

Example:

Say you've played 225 hours of 5/10 hold'em. You have a win rate of $9/hr (in that game), and a SD of 135(in that game).
Your overall SD is your SD (135) divided by the square root of 225. 135/15= 9.
This means (using the 3 deviation rule) that your real long-term exp. should fall btwn. -$18/hr. and +$36/hr.

It's worth separating all results by limit. For one thing I suspect your SD will be higher in bigger games. In my experience they are more often aggressive.

For example, my 5/10(with a full kill) SD hovers around a very managable 130. While my 10/20(usually played w/ a 1/2 kill) SD is a bumpier 325.

I realize this is daunting. It really takes a lot of hours to be sure of one's results. But this is the hard truth of fluctuations.

I hope this helps.