People tend to lose "sight" when calculating the moves in their heads.
When making a search for "blindfold chess" on the internet you soon find information that one of the most important advances in your chess life is to master the art of visualisation.

The Chess Eye gives you step-by-step exercises which help you to increase your chess visualisation.

Chess Eye keywords: chess, training, lesson, instruction, problem, problems, position, positions, vision, puzzle, game, visualize, calculate, calculation, visualisation, program, master, visualization, excercises, blind