I'm sure this question has been brought up plenty of times before, but could someone explain the concept of percent RPM on N1, N2 gauges? I have heard that 100% is intended to be the maximum rotation speed (since rotation speeds are so high in turbine engines), but if that is the case then why does the instrument go beyond 100% in most cases, and the green arc may sometimes even bleed a little over 100%? I'm surprised so little is explained in documentation or even in type rating classes (even the instructors are unsure in most cases!) especially when many pilots are transitioning from piston airplanes where RPM is actually denoted in revolutions per minute. Thanks.