To calculate P/E10, you need to use the Stock Returns Predictor.
Use the slider to enter P/E10. You can see the corresponding value of the S&P500. Then press calculate.
Repeat this until you come close to the desired S&P500 level.
[The predictions are based on P/E10. They remain stable. The relationship between P/E10 and the S&P500 varies slowly because earnings grow.]
Stock Returns Predictor