My original system, which still works great if you only want to trade a few times a year, is to take a 63-day average of any particular fund and subtract .20 from it. This is your "buy" point. Then take your 63-day average and add.30 to it. This is your "sell" point. You'll always make money and have fewer "bad" days. Just make sure you adjust your 63-day average every day. You'll always get .5 profit eventully. 4 to 5 times a year and your up roughly16- 20% for the year, depending on fund price, with minimal risk.
If you take the average for the passed 63 days, itis C:12.0, S: 13..1, and I : 13.4. If you take these prices, then the "sell" signal would of been, June 7th with C at 12.03, S at 13.06, and I at 13.5. As you can see, the S didn't quite make it to the high limit. That's because of the fear of rising interest rates like Tom said. That's why it might be good to take into account all 3 funds. Works great for the one day delay we have. because sometimes it will go a little higher the next day. May also go lower, but you won't lose as much as if you had stayed in a little longer and prices continue to drop.
Now taking this all into account, the next "buy" signal would be when the funds hit C: 11.56, S:12.66, and I:12.96. The prices may fall further, remember 2001 and 2002?, so you might want to set a lower cut-off for yourself where u get out and stay out till they start to rise again, or your 63-day average adusts accordingly. Make any sense?
I'm trading a little more aggressively right now, but I do keep track of this system.
PS- just saw on yahoofinance.com that the S&P vs fair value is +4.3, come on C fund!!