Notes on this puzzle
40 mines, 216 safe cells and one 16×16 field: that is Mine Finder #5209. Some cells only give way when two neighbouring numbers are compared.
The board starts with 93 cells already uncovered, 43% of the safe ground, so the first deduction is waiting for you. Under the cover, 52 safe cells touch no mine at all, 90 show a 1 and 52 show a 2; 22 cells carry 3 or more, and the highest number in the field is 4. 7 of the mines lie along the border of the field. Corners hold 2 of them; a corner cell has only three neighbours.
Where to beginWhen two numbers share most of their neighbours, subtract one from the other.