Notes on this puzzle
30 digits are printed in this grid and the other 51 cells are yours to fill. A solver that never guesses gets through it in 51 steps.
Most cells fall to the hidden single move: 50 of the 51 steps. Single candidate accounts for 1 more.
Among the givens, 5 is the most common digit (6 times) and 1 the rarest (2). The emptiest box is the top-middle one, with 2 givens; the central box is the most crowded, with 6.
Where to beginLook at row 4, column 2 first: a hidden single is available there from the very start. When scanning stalls, look for a cell whose row, column and box together rule out eight digits.