Adjusting my OG

Continued from other post( So over PM OG). So thanks for those of you giving me advice on my PM OG. I have been off on my last 4 brews by points. This last one, a high gravity ale really got under my skin as I posted a 1.070 and was shooting for a 1.087. I now realized that my mistake was not adjusting my reading for a 6 gal boil and 75 deg wort. Now I just need to know how to do that? How many points do I add for this? I normally don't take a reading, but when I did just for fun and I found out just how far off I was, I wanted to fix this problem. So thanx in advance for the info. Cheers

Primary: Double Arrogant Bastard
Primary: Red Ale
Secondary: Vienna lager
Bottled: Hefe Wheat
Bottled: 122 APA
Kegged: 90 Schillling Scottish
Up Next: IPA

Here's a link to a temerature correction chart for your hydrometer;

http://www.ebrew.com/primarynews/ct_hydrometer_temp_correction.htm

As far as boil gravity goes do this:

Take your pre-boil volume (v1), divide it by your post-boil volume (v2) and multiply that number by your pre-boil OG (OG1) This formula uses the convention of calling a SG of 1.070 "70" Thusly:

(v1/v2)OG1=OG2

In your case: (6/5)70=OG2
OG2=84 = 1.084

Or get Promash.