This is a trick i've been using for a while now on my iPhone 6 and it has to do with the speed of the fingerprint sensor.
I used to store 5 different fingerprints in each available slot (maximum 5 allowed) until i realized that if i store the same one in more that one slot, the reaction time would be a bit faster since i have two slightly different settings for the same finger. I've been using this for months now and i have noticed some improvement.
This also works on the 5S model or any iPhone with Touch ID.
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