Note: The "Look Inside" on the Kindle version shows much more than the "Look Inside" on the paperback version.This little book uses Tic-Tac-Toe to demonstrate a few features of the HP 35s scientific calculator. While the focus is on the HP 35s, many of the concepts discussed can be used with most programmable calculators. Equally important to the programming approaches are the proposed techniques for monitoring the moves of multiple players and the demonstration of a strategy for offensive and defense play. The HP 35s has 801 indirect storage registers and 26 direct storage registers. This book demonstrates the 'indexed' approach to accessing both types of registers. Although the HP 35s lacks a computer interface and a graphics display, it is reasonably priced at about $55 (July 2020). One of the attractions of the HP 35s is its ability to use Reverse Polish Notation (RPN). Its greatest strength is perhaps its capacity to store custom programs and equations specific to an individual's needs. The target audience for this book is the casual or infrequent HP 35s user wishing to expand their knowledge and use of the calculator - however, the book assumes no prior HP 35s experience. Explanations are provided for each command, along with the key locations - of which there are roughly 150 on the keypad. Note: This book does not cover every aspect of the HP 35s. Therefore it is important to have the HP 35s User's Guide which is available free online.http: //support.hp.com/us-en/product/hp-35s-scientific-calculator/3442983/manuals