1MARIO wrote:
"grand master preparation: calculation" by aagaard ...advanced with clear concepts....
http://www.qualitychess.co.uk/ebooks/CALCULATION-excerpt.pdf
http://www.jeremysilman.com/shop/pc/Grandmaster-Preparation-Calculation-77p3705.htm
Which is exactly why you need to work on tactics - the two go together, tactics training help you recognize and learn patterns, improving your combinational vision.