O.K. First a description of what you are looking at.
 
 "Sheet1" lists all of the colonisation options, in order of cost
effectiveness (i.e. the best ROR is at the top). The vairables are:
Enviroment (Benign, Hostile, Harsh, Desolate and Extreme)
Mineral content (Very Rich, Rich, Normal, Poor and Very Poor) - NOTE:
that as "Extreme" and "Desolate" can only occur as moons, there is no
"Poor" or "Very Poor" Desolate/Extreme options.
StMP - "0" is for insystem, "1" is for 1 StMP away, "2" is for
_exactly_ 1 month or less journey, "5" is for between 1 and 2 months 
journey, and "9" is for 3 months journey.

 Number of Asteroids - from 0 to 3 asteroid belts. I believe that you can
actually have up to 6 belts in a single system, but to reduce the size of
the spreadsheet I have limited it to 3.....
 
 Next is the colonisation cost, followed by the CFN cost and then to
TOTAL cost to emplace a PTU.
 
 Next comes the income per PU, and the "modified" income. The "modified"
income takes (somewhat) into account population growth, by taking an
average of the normal income, and the income after population growth
(assuming 25% growth for habitable worlds, and half that for
desolate/extreme worlds).
 
 The "modified" income is mainly there to try and judge between two equal
investments - it adds a slightly longer term view.
 
 Finally comes the turns to pay off the total cost, for both the normal
income, and the modified income.

 
 
 O.K. As I was in a modified GSF/R3rd ed campaign run by Andrew White, I
added the ability to change some of the constants. So "Sheet2" holds such
things as the colonisation costs, CFN costs, income modifier for
habitability, and REI multiplier. At the moment they are set for the
default R3rd ed, but you can change them to see what changes with
different figures.....
 
 Have a look, and if you see any mistakes, let me know. I am going to try and
set up a small page on the Fiction site for beginners, and this would be a
good start to post it.....