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: 48 of the 51 steps. Single candidate accounts for 3 more.
Among the givens, 1 is the most common digit (5 times) and 3 the rarest (2). The emptiest box is the top-right one, with 2 givens; the top-middle box is the most crowded, with 5.
Where to beginLook at row 3, column 1 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.