The Relative Strength Index (RSI) is a momentum oscillator that measures the speed and change of price moves. The RSI moves between zero and 100 and is considered overbought with a reading above 70 and oversold when below 30. Note the RSI can sustain an overbought (oversold) reading in a strong up (down) trend.
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You should clarify though that you are referring to the price of Yen in USD that is overbought, making the Yen itself extremely oversold.
Thanks, Patrick. We originally quoted yen/dollar but went with market convention..