Don't go by the name, this game isn't exactly a crossword. It's more of a modern version of "spot the difference". It's level based games themed around the notebooks of a scribe who jots down a lot of numbers in diaries and then ends up making mistakes in copying them from one notebook to the other.
The games comes in various levels.
To play the game in record time and to proceed each level, you need to scan through the pages of all three diaries and find the unique number in each of the three. Finding the right answers advances you to the next level and if you make a mistake you have to repeat the level once again. So get set and focus on those pages. It's a number's game !