Bartjens was a 'computer' in the original meaning of the word, i.e. a person doing computations. Therefore the game on the back of the Computer Museum's copy of Cyfferinge is an early example of a computer game! The game (a simple example of a magic square) is shown below.

"In conclusion, an amusing computation which always gives 24 whether the numbers are added along a diagonal, a row or a column.

For any other desired sum x, first compute y = x/3, then enter the following numbers in row order in the fields of the square: y+3, y-2, y-1, y-4, y, y+4, y+1, y+2, y-3.

The End"