YARDSTICK

[noun] [C] - a fact or standard by which you can judge the success or value of somethingIf the yardstick of success is popularity then he's undoubtedly done very well.You can measure a car's success by a couple of yardsticks - the number built, and the length of time it has been in production.Her performance of Cherubino became a yardstick by which all others have since been measured.