from m/s^2 to mm/ms^2

from m/s^2 to mm/ms^2   (09/13/2016, 4:14 PM)

To convert 9.8 m/s^2 to mm/m^2.
The answer is 0.0098.
We x by 1000 to get the mm then we divide by 1000^2. I was wondering why do we have to do the 1000^2. There is already a ^2 after the s? Thanks in advance.