The slowness is to do with the amount of map data that the unit is having to deal with. The class (speed) of the card only indicates its write speed, the read speed is the same, class 4 - 10. As the unit usually does not write to the card but only reads from it, the class is of no importance when it's used in the device. But it sure helps when you are writing large maps to it in a card reader.![]()
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