Bally's Yacht Club used a mechanism that was not used in any other bingo!
The numbers on the backbox are arranged in a 9x5 grid. By default, the second through the sixth column of numbers are surrounded by a yellow border. This is the card you are playing for.
If you earn the feature, you can move those yellow lines to surround a different set of 5x5 numbers! This changes the makeup of each row as you move the surrounds.
In my mind this is the precursor to the Magic Screen - just less expensive!
It was likely confusing for new players, which may have been why it was never used again.
