In this article, I would like to share my thoughts on the topic that is, for sure, extremely important for every chess player. That is how to calculate variations. Unfortunately, this highly interesting and crucial topic had never been covered in a great detail. The only decent source I know is the book of a Soviet Grandmaster Alexander Kotov “How to became a grandmaster”. However, it is quite evident that since it was written half a century ago, some ideas are not relevant anymore, the main reasons are that 1. time controls have been decreased 2. computers have changed chess world drastically.