How does ias work with each sword? Do they combine?

I've got grief one one hand and am contemplating Fury on my 2nd. I know dual grief is most damage, but is boring, and the mods on fury (ignore defense, 40 ias, deadly strike, open wounds, etc) is quite attractive.

Will the ias from grief and fury combine? Does it just affect the one weapon?

Thanks

In d2lod offhand wepon did not need any ias, it followed the main hand wepon.

This is how it used to be, unsure if anything changed:

Average WSM = (WSM1 + WSM2) / 2

EIAS or VINC or whatever its called on Frenzy:
VINC =FLOOR(70-AvgWSM-SLOW+SkillIas+(120*IAS/(120+IAS));1) (This is actually called Velocity Increase and does not have the 75 EIAS CAP, it has 200 CAP).

Frenzy FPA:
FPA =CEILING(256*17/FLOOR(256*VINC/100;1);1)/2

Double throw uses the same VINC, but slight difference in FPA:
Dthrow FPA =CEILING(256*12/FLOOR(256*VINC/100;1);1)
Then you devide that by 2 since both wepons are forced to throw. And wepon 2 is forced to throw before wepon 1 is thrown again.