Bingo has been played for many, many years. Traditionally, paper tickets were sold to players. As numbers were called out, players would cross the numbers off with a red marker. As things progressed, 'doppers' were introduced the game. These doppers put a circle of ink over the called number, making it quicker and easier to mark the numbers off.
To make the games easier, players generally mark on their paper tickets before the session begins what each games' theme is. If a game is playing CORNERS, the player will circle the four numbers needed on each game so that when the numbers are crossed / blotted out, it is easy to identify if you have won.
PETs (Personal Electronic Transmitters) are an electronic form of ticketing. Games purchased are loaded onto the PET prior to the session. The PET holds all the games you've purchased, as well as what the themes are for all the session's games.
A PET has a panel that has the numbers 1 - 90 listed on them. As a number is called out, you push on the number on the panel for it to register.
There is a display at the top of the PET that shows two out of all your games being played. The games shown are the ones that are closest to winning at any one time. It also shows how many numbers you have left to find on any of your games in order to win. When you have one number to go before you win, the PET will make a sound and display the number required to win. Should that number then be called, the PET will then display the word BINGO - prompting you to call out bingo to claim your prize.
Should you wish to play multiple sheets, the PET can be loaded with all these games too. When you push down on the called number on the panel, it crosses off that number across all games you have purchased.