ELO Rating system

Recognizing that I am not the longest tenured user here, I do not recall ever seeing any discussion of the ELO rating here. A quick search of this site didn't readily find any threads discussing it.

Being unfamiliar with ELO type ratings, I first went to Wikipedia to try to understand how it works. http://en.wikipedia.org/wiki/Elo_rating The mathematics behind it don't seem overly difficult. Since I am a firm believer that programming is a lot easier if one understands the math behind the problem, I would encourage you to study ELO ratings to make sure you understand how they work.

Based on the example in Wikipedia, here's one generic approach to such a spreadsheet:

1) You will need a data base that contains W/L/D/Rating information for each game played. If this is already built, you will work with the existing database. If you still need to build the data base, then you will want to structure it so that you can readily extract the results for a given player. I don't use Excel for database work, so someone else will probably need to help you with this.
2) I expect you will need a way to compute actual scores (Sa in Wikipedia article) for each player. If the database already contains the 0/0.5/1 values to indicate loss/draw/win, then this appears to be a simple =sum() or =sumif() (depending a lot on how you plan to query the database) function. If these values are not in the database, then a simple =IF() function or lookup function with a small lookup table should be able to provide these values for each contest.
3) You will need to calculate expected scores for each contest and a total.
4) If you want to be able to adjust ratings, then you will need to include an algorithm to compare the actual and expected scores and apply an appropriate rating adjustment.

I've necessarily left out a lot of details. If you will let us know where in this process you need help, I'm sure we can help you. A couple of tips for helping us help you:

1) Provide a simple sample spreadsheet that illustrates the input data, output data, and as good a description as you can give of how the output data was obtained.
2) Provide any math/algorithm details that you can. Don't assume that users here will know or understand the details of an ELO rating system. We are good at programming algorithms into Excel, but we are not experts in every mathematical model or algorithm.

Do you have any experience with other spreadsheets, or are you completely new to spreadsheet programming?

Along the same lines, if you understood nothing in my post, does that also mean you have no experience using an Elo type system?

If both of those statements are true, I would probably suggest you invest in some educational literature. There are several tutorials online and in print that will teach you the basics of how to use a spreadsheet -- how to enter data, how to enter formulas, etc.
A basic algebra text or tutorial (I like purplemath.com) would be useful for understanding the basic math being used in these formulas.
Wikipedia tends to be rather detailed in some of their explanations, so, if Wikipedia has too much for you to understand Elo ratings, I would suggest you search for a simpler tutorial for how Elo ratings work.
It is a lot to expect to be able to learn all of these things in a single internet forum post.

Here's a quick example spreadsheet I put together that illustrates the example given in Wikipedia's article (using Google docs, so hopefully it exports to Excel ok). Hopefully it shows you some basic spreadsheet programming strategies using the example Elo problem.