"In my defense... I saw 'Bring It On'..." -Anonymous Board Writer
Question #10663 posted on 11/24/2004 4:08 a.m.

Dear 100 Hour Board,

How come when a credit card doesn't read at the register it suddenly work when the cashier puts a plastic bag around it and then swipes it?

Confused Cashier

A: Dear Confused Cashier,

When swiped, the magnetic strip on the credit card generates a signal that is essentially a sequence of ticks that are read by the machine as digital zeroes and ones. Sometimes a scratch or a defect can cause a fluctuation in the signal that will be read as an extra tick if the card reader is sensitive enough. When you when you wrap the card in plastic, you're increasing the distance between the reader and the card. The extra distance is not enough to reduce the clarity of the normal magnetic signal beyond readability, but it is enough to smooth out those extra fluctuations from the scratches and prevent them from being read as superfluous ticks.