Formula for how much DME/LME to add when gravity missed

It would be very helpful to have in the tools section a way to determine the amount of DME / LME to add if you missed your pre-boil or post-boil gravity. 

For convenience, here's the info:

○ Missed Pre-Boil Gravity
§ Extract needed in lbs = (Total gravity(target) - Total gravity(from mash))/45 for DME, or 38 for Liquid extract
□ Total gravity is the volume of wort X gravity units of wort.
® Ie. 1.042 specific gravity = 42 gravity units
□ Example
® Total gravity(target) = 6gal (pre boil volume) x 64 (target pre boil gravity units) = 384
® Total gravity (from mash) = 6 (pre boil volume) x 42 (actual pre boil gravity units) = 252
® SO your equations with number is
® (384 -252)/45 = 2.93 lbs of DME
□ Pasted from <http://www.homebrewtalk.com/f36/formula-determine-how-much-dme-add-when-pre-boil-gravity-missed-185394/>

Shameless bump and clarification:

DME formula (uses the 45 divisor)
Pounds DME to Add = ((pre-boil volume * target pre-boil gravity points) - (pre-boil volume * actual pre-boil gravity points))/45

LME formula (uses the 38 divisor)
Pounds LME to Add = ((pre-boil volume * target pre-boil gravity points) - (pre-boil volume * actual pre-boil gravity points))/38

Yes, I went looking for that when I missed last time only to be left hanging. I thought it was part of the dilution tool.