Robert Ris has authored plenty of FritzTrainers for ChessBase — these are his newest, and perfect for every "Underdog" Calculation Training for 1000-1400 players Mastering these tactical motifs is essential to deepen your understanding of the game and become a better player. Calculation Training for 1400-1600 players Mastering these tactical motifs is essential to deepen your understanding of the game and become a better player.