you take a ski and carve it as hard as it can and still be carving perfectly (ie no skidding at all) in a complete circle. then, you take the radius of tha circle, (midpoint to any point on the circle) and measure it. thats radius. basically it tells you how well a ski can carve, how short of turns it can make.
and you can measure sidecut radius by laying your ski down on a piece of paper (the biggest piece of paper) and tracing the inside edge and you can use like a protractor or some formula to figure out the number if its not displayed, by the arc.
The Olson twins are Michelle you sick little baby fuckers.
its already been explained how to do it; its basically, if you have like below a 14 or so, its a slalom ski and will make you very quick turns. 14-18 or so is more like a gs or a crusier ski. anything bigger than 19 is smooth, as said before, but wont feel right when you first put it on