Just Checking G5:
Use Show all Notes and then use Erase Notes with no other actions inbetween
This achievement requires that you use Show All Notes and then immediately use Erase Notes afterwards. This can be done on any difficulty, but must be done in a standard Sudoku game, initiated from the Main Menu. Once the board loads, swipe up from the bottom of the screen (or right click if you have a PC) to reveal a hidden menu. Within this menu, you will find the two buttons required for this achievement. Hit Show All Notes and then Erase All Notes, without leaving the menu, to pop this achievement.