Question on combat values and fire values

[melm]

Hi all,

In the manual, I've read

For fire combat, the combat value is the adjusted fire value of the firing units. For assault combat, the combat value is the adjusted strength of the opposing side.

However, I have no idea how combat value is adjusted according to fire value(fire value I think I can get the value from L*S*E, and then adjusted by several effects). In manual, it gives an example using combat value = 400. How to get this 400? Can someone possibly tell me how to do the math? 

Thanks.