Features:
1) Based on 9 x 9 grids, divided into smaller cells, some cells are
pre-populated with digit 1-9, so people only need fill the other empty
cells, then make each row, column and region of the 9 x 9 grids filled with
different numbers since the number has thousands of arrangement
2) Product dimensions: 117 x 72 x 19mm
3) Power: 2 AAA batteries, number 7