After 6 years of taking the NYC subway, my First Swipe Percentage this year is still just 68%. pic.twitter.com/wNyfYRls9w— Nate Silver (@NateSilver538) May 20, 2015
He's talking about transit cards you wave or tap against a reader at a turnstile. I'd say my first wave/swipe/tap also works about 70% of the time, though I never counted. I probably get second tap failure about 10% of the time. It's something you notice because tap failures can cause you to miss a train you're hurrying to catch.
Perhaps a more useful measurement would be to monitor a randomly selected group of turnstiles in the system, counting first swipe percentage for all users.
Why not shoot for 100% first tap success? I imagine that reader sensitivity would have to be increased to a point that it would cause accidental charges.