Dennis they are not identical and I’m sure calculating the interest variance has been around a long time.
I do have another way to do this based the price action location in relationship to the 200 SMA where a trader builds a chart with the pairs list down the left side and the currencies listed across the to row. Then you would place a 1 or zero in the appropriate currency/pair column based on above or below the 200 SMA.
But I am a lazy trader and that is time consuming work. And the top kine of that chart from FX gets me several hundred pips per month in my Longer Term trades of 16 hours to 3 days and well within my risk limits of 1% per trade and 2% per account total trades.
For me that is KISS to the max!