22:34 Nov 26, 2011 

But then to find the circumference you need to evaluate an elliptic integral, which has no closed analytical form.... Ha ha. But isn't the whole sentence overly complicated? Isn't it just the arc length of a circle corresponding to an angle of 45°?

21:19 Nov 26, 2011 

@Chris - thanks for the info! But I changed the figure in fact for the sake of disguise, so I must dash any hope that they are reverting to a splendid Imperial "référentiel"...
@kashew - I did scour the archives here before concluding that nothing fitted the bill satisfactorily and I needed to pose the question... I'd call this quite an elliptical expression in FR, hence perhaps the befuddlement.

16:03 Nov 26, 2011 

is right - and this is already on Kudoz - at least once.

13:09 Nov 26, 2011 

in geometry is "to project or roll out (a surface) onto a plane without stretching or shrinking any element". Here it just seems to be describing the curved section resulting from an angle equal to 1/8 of the circumference, which, with the numbers given, results in a diameter of 25.4mm ie. 1 inch exactly.