Notes on this puzzle
36 digits are printed in this grid and the other 45 cells are yours to fill. A solver that never guesses gets through it in 45 steps.
Nothing beyond hidden single is needed anywhere, so the whole grid is a scanning exercise.
Among the givens, 1 is the most common digit (6 times) and 3 the rarest (2). The emptiest box is the top-left one, with 3 givens; the top-middle box is the most crowded, with 6.
Where to beginLook at row 1, column 2 first: a hidden single is available there from the very start. Scan digit by digit; notes are hardly needed here.