RSI is measured on a chart between zero and 100 on the Y-axis and time on the X-axis. The RSI meaning of a drop to 30 or below indicates the stock is in an oversold condition. The stock RSI, meaning on a rise to 70 or higher, indicates an overbought condition. Be aware that just below a stock is under the 30-band doesn't mean it can't go lower.
Many traders make the mistake of buying a stock when it falls to the 30-band as it continues to fall lower. An oversold stock can continue to be oversold as shares drop. The wiser entry would be when the stock returns through the 30-band when the reversal has formed. The same applies to traders who short-sell a stock just as it hits the 70-band and continues to make higher highs. Remember, just because a stock rises through the 70-band doesn't mean share prices can't increase.