True dat.I thought I would start by pointing out that adding unit point values until you reach the limit is actually exactly the same as removing the value of each unit from the total available until you reach zero. This is in layman's terms merely a question of 'reversing the polarity'.
To try extrapolate on the topic a bit:
I have folders on my PC for each army I own.
In there, I create a text document with everything I own of that army. Example: 6 marines with bolters, 2 lascannons, 1 marine with powerfist, 1 snotling picking his nose etc etc.
I then create a spreadsheet in that same folder. (Excel / Open Office).
In there, I make a number of columns: Count, Description, Point cost, Total.
In Total field, I do calculation of "count x cost" or, to be correct "=A1*D1"
So, starting at the top I would type something like:
1 Lord 9999 9999
10 Marines 400 4000
The last values are filled in automatically, due to calculation.
At the end of this I do a sub total on coloumn D (the total points one).
I build on this to make a huge list with everything I own, and it's associated points cost. This adds up to a total. I can then decide what I don't want in, and make the count 0. Removes it automatically from the total. When I print the list out to take to games, simply hide the rows that are 0 count.
I can then also add things like:
10 Marines 400
1 Aspiring Champion 300
1 Powerfist 3002
1 Icon of Happyness 150
(note, these are obvisouly dummy points values, due to rules. If I have a powerfist of 3002 points, it damn well better take down a titan on first hit).
It gives me a good breakdown of what the person has. Sometimes I'll go so far as to type out ALL the possible options giving them the points value. That way simply fill in a 1 in the first coloumn and it's selected automatically.
I take this whole spreadsheet further. I have workbooks along the bottom with dates. So, lets say a config didn't work well I can make notes, make the next date for the following game and change the list. This allows me to keep a history of what I've made, and track the changes in case I want to go back to trying something.
If this is as clear as mud, let me know and I'll try explain it a bit more.