This book, 'Introduction to the Soroban', is a powerful aid in the understanding of number.
This book is an introduction to the use of the soroban, and is printed by a British mathematics teacher society (Association of Teachers of Mathematics). It was written chiefly by Kimie Markarian. She has undertaken to introduce the soroban to the UK, and has been active for many years. It has lots of exercises.
Moreover, it introduces 100 gem abacus at the beginning of the book. (introduction only of addition and subtraction)