Keep a chart of all your trades in excel. This should then allow to then run calculations like win%, number of winners and number of losers. This can also tell you total profit amount and total loss amount. It can also allow you write thoughts next to your trades. I usually will write why I am taking the trade, if I won or loss, and then summary of what went right or wrong. I also will end of day, write what I thought of day. It may help you see a common mistake you keep making to improve your win%. Also, many programs like ninja trader and trade station have reports that you can generate that will provide many good statistics for you.

net p/l imo there must be zillion other more sofisticaded ways, but they all end up in that figure, either there's some ( edge ) or there isn't ( negative ) regards

I see what you're saying, but its always possible your p/l is due to random luck rather than a true edge. My question is how do you determine weather you are lucky or good?

No, it's not he profit factor. the Edge is well-defined and equal to how much your system has won on average: Edge = avg. win x success rate - avg. loss ( 1- success rate) Easy to calculate with excel. The edge divided by the avg. win is the optimal bet size. Ask any gambler. See this paper for details.

disagree. Profit Factor is an excellent measure of an edge. Max drawdown and Sharpe/Sortino is also useful.