Originally Posted by
FBinNY
Chain checking gauges tend to read high for a number of reasons which I won't bother going into. Measure your chain the reliable old fashioned way, as described by JoeJack above, and replace it if stretched beyond 1/16" over 12". The rate of cassette wear increases as the chain wears, so the per mile cost of running your drive train increases using old chains.
I'm not a fan of using a flat mileage basis, since the chain wear rate varies so much person to person, with some burning out chains in a little over 1,000 miles and others going for 5-10,000 miles. Everyone rides differently, under different conditions, and has different attitudes about chain care, so averages are meaningless to you're own situation.
BTW- follow good chain lube and care practice to maximize your chin life, and that'll save you dough on cassettes also.
Along that note. Once you've ridden consistently enough and o regular maintenance on your own stuff you get a rough idea on how long a chain should last. Whether it's one end of the typical mileage extreme or the other, or somewhere in between. Ini other words get to know your bike if you're intereste in taking care of it. Also chains wears in more than two ways. Lengthwise an 'width' wise across the rollers. A chain may measure fine but show and act like an extremely worn chain with roller wear.