Ignore the first card and on the second card, count "one" in your head. Continue counting cards as the spectator deals them onto the table. When the number that you count matches the value of the card that's called out, this is the spectator's card. In our example, when you silently count "seven" and the spectator calls out "seven of diamonds," this is the spectator's card.
Note that occasionally the trick will identify the wrong card, which is simply by chance. In this case, if the spectator says you have the wrong card, just have him continue calling out cards as you silently count to yourself. You'll eventually come to the spectator's card.
