Is there a way to write a custom formula that would gage the RS of one ticker against another for say a 10 day period?  Lets say I want to compare the RS of AAPL vs SPX for the past 10 days and then I want to compare the RS of AAPL vs AMZN for the past ten days.  Is there a way to do that, or do I just have to compare their RS to the SPX?

Thank you!

No, there really isn't any automated method of writing formulas for Relative Strength.

You can plot RS on the chart and change the symbol against which the active symbol is being compared by just editing its settings.

If you want to change the numerator to something besides the active symbol, you would need to add the other symbol to the chart as an indicator and change the Data Source to use this indicator for the other symbol instead of normal price history on the chart.

If you want the comparison to be over a fixed number of days, the best way to do this is to add a Rate of Change Percent indicator to the chart and change its Data Source to use the RS indicator instead of price history.