Had to shoot some Provia 100f at 400 yesterday, that means it's time to get to know pushing in E-6.
With APUG down for a while I googled and found two suggestions as follows.
Add 2 minutes for 1 stop and 5 minutes for 2 (9 and 12 respectively)
Another suggested a 36% bump in time for each stop so, 9:30, 13, and 17:30.
I didn't find any numbers on APUG via search so I figured I'd ask.
Are these any where close?