odds of spending x time in losing ground

This is a simple math question, although the answer, I don't how simple to get to.
my question is how to calculate the probability of spending x number of hands at a loss, or at a negative standard deviation if you prefer.
thanks in advance for any response

It sounds like you are looking for the probability of being behind after x hands (or hours, or any other unit of measurement). This should get you started:

http://www.blackjackinfo.com/bb/showthread.php?t=4891

-Sonny-

didn't read sonnys link as I'm on a mobile, but the op might also want to look into a concept called N0 (N zero), which details te calculation of the number of hands or time needed for your EV to exceed a stated number of standard deviations. Would link to a thread but am working of an iPhone.

You do realize it is quite posible to still be ahead in dollars from orig roll yet be experiencing a minus Stan Dev from EV?

Basically, 2 completely separate questions.