Notes/pencil marks are small numbers that you can enter into cells when you aren't yet sure of the final answer. If you sign into your online account on multiple devices - your desktop and phone for example - and open the same puzzle on both, only the one that opened it last will be able to save it.

Killer sudoku | Lifeandstyle | The Guardian

A puzzle's difficulty level is estimated when it's generated, whereas the average solving time is the result of people solving it. The difficulty calculator gets it right a lot of the time, but ultimately it's only an estimate and so there are occasional disparities.

As you browse through the archives, you'll be able to see which puzzles you've solved and your solving times. Patreon

Killer Sudoku online - Solve daily killer sudoku puzzles

This can happen with multi-cell selection. It means that some of the highlighted cells contain the value and some don't. So, for the button above, only some of the highlighted cells contain a 6.The FILL button (or F key) enters all numbers into the highlighted cells. If fill uses cage combinations is enabled (via the Preferences menu), then it only adds numbers that appear in the respective cage combinations, otherwise it adds all numbers from 1 to 9. I've made a lot of improvements and I'll continue to make them over time, so hopefully any differences should become fewer and further between! Why can't I see printable puzzles?