Check new chains with any chain checking tool before relying on it for anything. As a former pro Buyer for a chain of shops, I have seen many mechanics make a fool of themselves by using a chain checker on every bike they encounter and then telling a customer that their barely ridden bike is in need of a new chain soon. If your chain checking tool fails to show new chains as such, you are convoluting accuracy with precision. If all chains run a little long, measuring them to the shorter specification is worthless. The only relevant measure is the baseline length of the chains you purchase and not their accuracy to a published standard. The fallacy of chain checkers is the relevancy of the standard.
As of 2014, I tested most chain checkers that are regularly available from the major distribution channels like QBP and Hawley. None of them consistently measure Shimano, SRAM, or KMC chains as new using new stock in a store.
The only use I recommend for chain checkers is when you have one for yourself. Measure your new chain and write down both the locations of measure and the measurement. You need to use the quick connect link or the press pin as a locator to measure a few links ahead of and behind. This creates a deterministic way of measuring the stretch over time in a useful way. Since accuracy is rubbish, and only precision matters, your choice of tool is only relevant in how well it can repeatably indicate the same level of precision.
The underlying issue is that there are no checks or regulations that enforce the standards accuracy of bicycle chains, or cogs for that matter. If there is such an authority that I am unaware of, as of 2014, it was wholly and grossly ineffective. Any chain checker that tries to pin a floating value to an accuracy measure is assuming a calibrated and regulated standard.