Hidden Single

Pick a unit (row, column or box) and a digit that is not yet placed in it. If only one cell of that unit can still take the digit, it goes there, even if that cell has other candidates too.

Example: in box 5 the digit 7 is blocked in every cell except r5c6 because of 7s in other rows and columns. Then r5c6 is 7.

Tip: Scan one digit at a time across all boxes. This is the most productive habit for easy and medium puzzles.

Notation

Hidden Single: 1 goes in r1c4.