NEW YORK ( TheStreet) -- When you invest in a market that is extremely overvalued fundamentally, momentum trading takes over. When you employ a buy-and-trade investment strategy for a specific stock the reason to buy does not have to be based on valuation, it can be based upon momentum. In either case you use a good-til-cancelled limit order to buy weakness to a value level and once long, you use a GTC limit order to sell strength to a risky level.On Aug. 23, I wrote Apple Has Mojo, Google Does Not and this was after Apple ( AAPL) ($467.71) became overbought on its daily chart and had tested my annual pivot at $510.64 on Aug. 19. Buy-and-trade investors thus had the opportunity to book profits at $510.64 as an annual risky level. To keep its mojo status Apple needed to have a close above $510.64, but that did not happen. www.ValuEngine.com with fair value at $453.97, which makes the stock 3% overvalued. My annual value level is $421.05 with the ValuEngine one-year price target at $492.12. AMZN) ($299.64) declined from an all -time high at $313.62 on July 27 to $279.33 on Aug. 28, and then momentum began to rise on its daily chart. Amazon fell below its 50-day simple moving average at $290.59 on Aug. 15 and today is back above this key level now at $295.46 trading as high at $301.86 on Wednesday. The weekly chart is neutral with declining momentum but with the stock above its five-week modified moving average at $292.69. Amazon has a hold rating with fair value at $246.96, which makes the stock 21.3% overvalued. My quarterly value level is $272.68 with the ValuEngine one-year price target at $297.47, and my semiannual risky level at $313.60, which was tested at the July 27 high.