GG - you've got it figured out.
I'd be a bit careful quantifying the declaration of RPD (I use Rev Per Foot in my graphs) - 8 or 9 decimal places might be understating it. The translational deceleration is at least in the thousands of times higher but I'm not sure it's billions of times higher. ( It might be, I'm hoping someone can provide a reference to this ).
I looked at some sub-sonic flow papers but they used square plates or tubes to test theory vs. measurement (besides we don't care about sub-sonic)
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the actual measurement of the RPD's in relation to the RPM's, velocity, and distance
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I've posted Buf Bob's data of RPF (RPD) vs Vel and RPD vs Distance at RPM_RPD
be sure to select "Sheet2" on the bottom right of the page.