Make interactive tutorial (learn by playing)

Guess Moves

We need to add a state at a number to say the piece is sure, or the piece is not sure. Currently this one is red, so I could remember I may have to delete later But it don't stay red

Create "hint" button

Add an indicator for move mistakes

How do I know that my number is in the right cell? it’s so difficult to figure out where I made the mistake as soon as I make it

Timer

add a timer to measure our success and to try and beat our previous record to complete

Visual Tutorial

I think you should show a completed puzzle with all squares filled in. And then a few colored highlights in that puzzle displaying links that go horizontal, vertical, and diagonal. Many of us are visual learners and it would be easier for newbies like me to see the concept in this completed format.

Fix double tap issue causing zoom-in (mobile) during gameplay