A Google user
When you start this Mathdoku app, The Back-Key of your Samsung phone becomes inoperative.. (when you turn Mathdoku off, the back-key works again). you need the back-key in order to make calculations, like finding the factors of a large number.. But what is most annoying is the fact that the Mathdoku program does not give you any service (like revealing the value of a cell if you feel you cannot proceed otherwise) or any feedback about what you are doing: You can fill the grid with fully nonsensical values without any reaction from the app. It does not indicate how long you have worked.. it does not erase the temporary pencil marks when they are replaced with final values..
Verschueren Geert
10 June 2019
Thank you for your honest review. Do you mean the triangle back key? This is done to avoid accidental closing. You can use the circle to temp. exit the app during gameplay.
If there is a lightbulb under the grid you can use it to fill in a value after watching a rewarded ad. Auto pencil removal is not right as you might've made an error somewhere.