Number of hands needed to judge profit?

[Pappy25]

How many hands do you think you need to play to acurately judge if you are actually making a profit. I have created a spreadsheet and am keeping track of the date, time played, hands played, profit, profit per hour and a cumulative profit and profit per hour. Anyone else doing similiar? and/or have any suggestions or advice. Also, can someone explain standard deviation or point me in the right direction on where to read about it. Thanks.