NoteworthyG 5

Noteworthy G5:
Enter more than 100 Notes

Notes only count towards this once you complete the puzzle you make notes on.

So start an Easy Classic, use the note button to make a note of every number (1-9) on every blank square, then complete the puzzle. This should pop after your first puzzle and will also get you about 70% of the way towards the “Notary” achievement for making 500 notes.