Answer: Presumably you mean how the value would change if the 6 were replaced by a zero.
In that case, the value of the 6 is 6/10, the value of the 7 is 7/100, and the value of the 8 is 8/1000.
Explanation:
0.679 = 6×10^-1 + 7×10^-2 + 9×10^-3
= 6/10 + 7/100 + 9/1000