Trachtenberg System of Mental Calculation

When working with it, it is actually rather limited compared to other systems that were around the same time.

There is a far better and more robust system that has been reprinted several times, which was aggregated in a book more recently, called "The Cosmic Calculator", this is a three volume series for teaching mental math to kids, based on the ancient Vedas teachings, also called Vedic Mathematics.

It is at least 20 years old, I still have my copies that I received in 2001 as a gift, Amazon says it was published in 2019 which is incorrect; it is far older.

It was often used alongside activities where you would memorize (via flashcards) the common complements for 9 and 10 to the point of instant recall/association.

The digit sums are somewhat lacking, although understandable considering that the fundamentals of abstract math and group theory were still being explored at the time of publication. (i.e. digit sums cyclic groups).

You can find a link here. For reference, the copies I received in 2001 are identical to the displayed version below. There is also a Instructors Manual (a 4th book) which came with the set.

https://www.amazon.com/Cosmic-Calculator-Course-Mathematics-...