In the past, I have written about cart machines. If you have not been in radio you may not have ever encountered "the cart machine". These are now obsolete, but I will bet, somewhere in America there is a station still using cart machines. If you know of one let me know. For those of you who are in the dark here is a video of a cart machine in action. On thing, the board being used has slider faders. In my day the knobs on the board were round, mechanical, and a source of problems.
And here is a "old style" board: