What are ALL the variables necessary to calculate Accurate ROI in the mining biz

[Sage]

I'm looking to do some hardware purchases, but need the hard numbers to plan out the mining biz...

Does anyone have an accurate formula or spreadsheet to start with?  I imagine the variables to be:

- Current difficulty
- Projected difficulty increase and dates
- Rig speed
- Hardware upfront cost
- Hardware maintenance cost
- Bitcoin price
- Power consumption
- Price of power

Am I missing any variables?

Primary question right now is how to calculate possible coins recovered based on current difficulty and Rig speed?

Any advice here would be most appreciated.

[Rawted]

http://www.bitcoinx.com/profit/

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allchains.info

should answer most of those questions!

[Gator-hex]

http://www.bitcoinx.com/profit/ to figure it all out and latest bitcoin price and difficulty.

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https://en.bitcoin.it/wiki/Mining_hardware_comparison for Mh/s per $ and W

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http://www.ebay.com for prices (Ati 5830's are lowest $/ROI in my opinion)

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add 100w if it's going in a PC for all the other PC stuff

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your electricity bill should tell you the price you pay for KW/h