in the case of division, the sequence is important, as a/b/c is NOT equal to c/b/a
the same is true of subtraction, namely order is important as a-b-c is NOT equal to c-b-a
in your example, 777/888/999 = 0.000876 whereas 999/888/777 = 0.00144
and 777 - 888 - 999 = -1,110 but 999 - 888 - 777 = -666
in both addition and multiplication, the sequence is unimportant, as a+b+c =c+b+a; likewise, a*b*c = c*b*a
in your example, 777*888*999 = 999*888*777, and 777+888+999 = 999+888+777
I am sorry to say that I have no idea what you meant by "diagonally"