Back testing is a way to see if your trading system is profitable, by using historical data. Recently, I came across a back test of one such system on a blog, and the owner claims that it works, based on a period of one year. I only have one comment, that is, if it is really works, it should work over and even longer period. Nonetheless, I understand that every system has certain precepts, which I am not clear about. Off to the doctor again!