Many chain checkers are not accurate - more a screening tool than an measurement device. A ruler is simple and accurate. No idea at all of pedaling rate? Is it close to one rev per second (60 rpm) or significantly higher? What gear combos do you ride in most of the time? Preferably the 50/11 and 50/12 combos should be used only when going downhill, and even the 50/13 would be on a very, very good day on the level for short periods of time (20+mph at only 70 rpm). Even the 34/11 is a pretty high gear (about the same as a 50/16) best for going over 18 mph. In addition the small chainring and smaller cog combos will wear the chain and cogs a bit faster.