[r9etb]

Um, you could measure the radius and the diameter of a circle, but it is the ratio of those two values which nets 'pi' and you cannot write the last digit of pi, unless you've discovered something i'mnot aware of.

It is nevertheless physically measurable (within the limits of the measuring device), which means that it's not an "abstract" quantity in the normal sense of that word.

[MHGinTN]

I meant to write ‘radius and circumference of a circle’ ... doing too many threads simultaneously.