Variations on Advanced Sudoku Logic Puzzles (Vol 1) 
 Chapter 22: Four Medium tpsmith Puzzles (numbers 69-72) 
 
-  Step-by-step instructions for solving  Puzzle 69, (74/144)   Diff: 6/99.9991
 -  Step-by-step instructions for solving  Puzzle 70, (79/144)   Diff: 6/99.9993
 -  Step-by-step instructions for solving  Puzzle 71, (81/144)   Diff: 6/99.9995
 -  Step-by-step instructions for solving  Puzzle 72, (84/144)   Diff: 7/989.9998