was the first to experiment with a prism device built into the table to check beneath tens for dealer naturals. The device is called MAXTime. When the dealer gets a ten up, he simply slides the cards over MAXTime, and through a small window is able to view the corner of the hole card. Aces are marked with the letter "A" in all four corners. If there's an ace in the hole, the viewing window displays the A. If no ace, the window displays plain white space. Dealers know immediately if they have a natural, but have no additional information concerning hole cards that are not aces. This method of checking the hole card is now being used in several casinos.

From the Las Vegas Advisor site.