ratios.
So: pi: ratio of the circumference of a circle to its diameter.
Rate:
A rate is a special form of ratio where the the two terms are in different units. 
a circumference and a diameter, despite both being “of a circle”, is it possible that we are using the wrong units for circumference?
this would make sense because the shape of the “line” of a circumference is different from the shape of the line of the diameter:
The underside of a curve is different from the outer side of a curve.
but there is no difference between the underside of a straight line and the outer side of a straight line.
i’m stating something obvious probably: it sounds like this is what calculus deals with – but perhaps a rate is needed instead of a basic ratio.


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