Originally Posted by
Tourist in MSN
I would need really strong reading glasses. Over a 12 inch length, 12 1/8 would be 1 percent, 12 3/32 would be 0.75 percent.
I used to do this with a 36 inch steel ruler but it was a hassle to take the chain off for a measurement. Then I bought one of the better chain checkers.
Yeah, when it is off the bike measuring a longer section is great, but these days I pretty much never take the chain off the bike other than to replace it.
I suspect you are trying to read with more precision to an actual value than I am. For me a quick look shows a reading of 12" or noticeably more than 12". That is close enough to know whether i need a closer look to get an accurate reading if desired/required. The thing is that typically I have found that once they start to go they go pretty quickly so once they show noticeable wear I keep close track or just replace it.
A good indicator that doesn't require reading small calibrations on the ruler is to use half a pin as the maximum allowed "stretch". So a 12" rule or a 12" piece of metal with no calibrations works okay for me.
Also with a thin 12" rule like a Starrett machinists rule you can tell by feel on the pins if it is exactly 12", slightly over, or well over.