Full House
Level: Basic
When only one empty cell remains in a unit, fill it with the last number.
A Full House is when a row, column, or box has exactly one empty cell left. Place the missing number from 1–9 in that cell.
It's the simplest confirming technique, and it often shows up late in the game or in units that are nearly complete.
Use it after another technique has nearly filled a unit — it's a quick way to finish it off.