the old way of doing it involved cupping your hand around the card and trying to look at the card discretely. The issue is someone could be standing behind you

the old way of doing it involved cupping your hand around the card and trying to look at the card discretely. The issue is someone could be standing behind you and get a glimpse. Not to mention with the old method the dealer would actually see their hole card. Let's say the dealer shows a 10, then when they check, they see they have another 10 as their hole card (face down). The dealer could intentionally or unintentionally give away what their card is, causing someone who normally wouldn't hit on, let's say 17, to take a hit, since the dealer would beat them anyways. With these little windows, the dealer only see IF they have a blackjack, not the actual card itself. This happens because the markings for 10s (10, J, Q, K) are all offset slightly to the right. Then the Ace is offset slightly up (the dealer turns it before sliding it into the window). I use to be a casino dealer. (edit: typo)