Quote from Robert Weinstein:
You asked..... Standard Deviation
to quote my brother "I wouldn't worry about it"
calculating gains/losses on a daily basis puts you on a roller coaster that you don't need to be on and will probably do a lot more harm than good. If you have 50 wins for $100 and 48 losses for $100 you will end up a net winner BUT emotionally you will be drained as you may feel like you have lost as losses feel worse relative to an equal win.
If you want to calculate your gains/losses I would suggest thinking about doing it on a period of no less than a month or better yet for the year. Don't drag the weight of everyday on your back when an equal amount of focus can go towards improving your trading skills and that time will add to your yearly results....
Ok, back to my studying...