I used to perform this all the time years and years ago and found it this evening in a box in my closet. No instructions. I can’t remember the formula but you’d have someone roll the bars and line them up add the numbers and you’d tell them the number before they could write it. To my recollection you looked at the third row of numbers but I can’t quite remember it all.

Anyone know?

Thanks!

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Hello Jonathan,

Most people refer to these as the "Mental Logs." They date back over a hundred years and have a rather interesting history, both in the US and in Germany. I've written a ton on these (history, how to customize, make bigger ones, etc.) in this thread:

https://www.themagiccafe.com/forums/view......forum=82

However, until you hit 50 posts here, you won't have access to that source yet.

Meanwhile, I sent you a PM which answers your question about the procedure.

Thomas Henry

Thank you so much for the response!