All magicians who have bought and use the addition slate invariably do it the same way. I used it twice, up on the northern peninsula of Michigan, back in 1927, but stopped for two reasons. One was that I had personal reasons for not doing it, and the second was that everybody hopped on the band wagon when it was first sold, and made it too common.

Dr Daley doesn’t like the idea of prophesying the total, so evolved an entirely new presentation. Have four people stand. Each is to think of a four figure number. You hold a slate and looking at each in turn, write a line of figures on the slate, but let no one see it. Now you draw a line, and can be seen running up the columns and writing a total underneath, at the bottom. You actually write anything in the four rows, but do put down the correct total which later will be arrived at.

Now you erase, without showing, all the figures except the total, which you show. Place the slate, with the total outward, where all can see it continually.

Pick up the other slate (faked), and pass to each of the four standees. Each writes his four figure number, and a fifth person adds. This person stands and calls out the total at which he has arrived, the audience being able to see and check it with the total that has been left in full view throughout.

This makes a really logical feat of mindreading, and your actions at the start are what you’d actually do if a thought reader. It would take a super-mathematician to get 16 figures in his mind and add them instantaneously. You are a mindreader; not a rapid addition man. In this presentation, you have gone about reading the mind of each spectator, jotting down the numbers that they, evidently, are thinking about, then very humanly and naturally adding the figures as anyone would necessarily have to do, and have arrived at the total which you put in view. The audience figures are written, added by someone else, and the total proves you right.