Hey, I'm from Ask Mr. Robot. As a previous posted stated - Mr. Robot does math for you. And it's all based on the stat weights. We provide default weights, and for a lot of specs we have 2-3 default options (look in the drop down menu, below your character name).
If you don't like any of the presets, you can customize the weights and Mr. Robot will re-optimize everything. Don't forget about his gem optimizations - he'll calculate which socket bonuses are worth getting. That math isn't too hard, but hey, he does it all in under a second!
It's also important to know that the stat weights drive the item rankings. So be sure you are using the weights that you want to, so the gear rankings are relevant.
Here's some more info you might fight useful:
- Pre-Optimization overview: http://blog.askmrrobot.com/wp-content/uploads/2013/04/Overview1.png
- Post-Optimization overview: http://blog.askmrrobot.com/wp-content/uploads/2013/04/Overview2.png
- Options menu: http://blog.askmrrobot.com/wp-content/uploads/2013/03/OptionsMenu1.png
- Editing stat weights: http://blog.askmrrobot.com/wp-content/uploads/2013/02/EditStatWeights.png
- Relative vs Absolute gear rankings: http://blog.askmrrobot.com/wp-content/uploads/2013/02/Absolute_vs_Relative.png
If you have any other questions, let me know. Happy to help :)