Notes on this puzzle
27 digits are printed in this grid and the other 54 cells are yours to fill. A solver that never guesses gets through it in 59 steps.
Most cells fall to the hidden single move: 54 of the 59 steps. Pointing pair accounts for 5 more.
Among the givens, 4 is the most common digit (5 times) and 3 the rarest (1). The emptiest box is the central one, with 1 given; the top-middle box is the most crowded, with 4.
Where to beginLook at row 5, column 6 first: a hidden single is available there from the very start. Pencil in candidates for one box at a time and watch for two cells that share the same pair.