130% PE Expansion is taught by Bill O'Neil in some of his seminars.
The general procedures is as follows:

Pick the first institutional quality base coming out of a bear market. This usually means the price is above $10 and there are some earnings. Look for obvious volume clues as an indication of institutional activity. Find the initial breakout from this base and on that date you write down the PE. I keep the electronic version of Investor's Business Daily on my hardrive (back to January 2003). I can then look up historical PEs in the stock tables. Multiply this PE by 2.3 (same as adding 130%) and then multiply by future earnings estimates 18 months to 2 years in the future. This is your price target. For large cap stocks you can expand by 98% instead.

Now that you have done this you are not flying blind as to what kind of gains the market supports on a historical basis. When approaching a price target on a position you hold you can tighten up what ever mechanism you use for selling positions with some assurance that the upside potential is now limited.