okay let's say you have a lvl 18 war

and you want to lvl up your subjob. You want to get it at least so lvl 9 that way you won't be 'gimped.' So whatever your main job is at

ex: war 20
-monk 10

whm 30
blm/rdm 15

just some examples. That's what he meant by halving it. *Cutting it in half*