Introduce an Indicator to Decide When to Buy/Sell

Most of tigers want to learn about how to decide when to buy and sell stocks. We really need brilliant tigers to help us answer this question! ----- [TOPIC] Introduce one simple indicator to help us know when to buy and sell. [FORMAT] Explain 1. what is this indicator? 2. how to use this indicator? 3. what is the risk and advantage of this indicator? ----- [REWARDS] 1. One post with the highest quality will get a $10 stock voucher. 2. Three posts with the top 3 likes will get $5 stock voucher. 3. Every valid posts above 50 characters will get at least 50 tiger coins.