In short, it is using past history record to project future price. Then depends on your target return rate, today's worth can be calculated.
EPS and PE are 2 critical data needed to use that system. In case you don't know where to get these data, refer to one of my old post here : where to get EPS, PE data
For those who are more curious to ask why more than just using the system, an old post explain slightly why use EPS and PE in stock valuation ?
I haven't published this system yet and only using it on my own now. But if you are interested, you can also use it from here ...
I am thinking to publish it once an anonymous browser can sign up as an user in order to use it ....