Space sum app for iPhone and iPad

Space Sum is a logic puzzle that challenges thinking strategies. The objective is to fill up a 5 by 5 grid with the numbers 1 to 5 so that they appear only once in each row and column. Each circled number shows the sum of 3 numbers that they touch with the green lines.
The interface is user friendly. One touch on the top row of numbers and another touch on the destination square is all that is needed to fill up a square with a number. A touch on a number on the grid will erase that number. This fast and simple interface ensures a smooth action so that the focus of the user is on the thinking process.

At the top of the screen showing from left to right:
1. instruction button
2. rewind button
3. reset button
4. forward button

RESULT
Once all the 25 squares are filled, if they are correct, an animation sequence will be activated and the reset button becomes the ‘next’ button. If the user has made a mistake or more, the error will be highlighted in red circles. The user can then try to repair it or just press RESET and try again.

PUZZLES
The puzzles have been carefully crafted and sequenced from easiest to hardest. The user has to solve each puzzle before the next puzzle is made available. He can of course re-solve puzzles that he has solved earlier. If the user simply uses trial and error, it would be difficult to solve the puzzle. Logical step-by-step deduction is key to the solving process. Each puzzle has one and only one solution, the prerequisite for a good logic puzzle.