If you want to use an OSR compatible supplement with Retro Phaze you will need to do some converting to make things work.
The key score you will need to convert is Armor Class.
For the most part, the quick and dirty rule for converting D&D Ascending Armor Class (higher is better) to Retro Phaze Defense is: Armor Class divided by two, round fractions up, and then add one to the result.
This is a pretty quick and easy formula for the Ref on the go, but it doesn't always work when comparing AC to actual RP armor values, so the graphic above includes a table with the true conversion values for when you need to be more accurate.
If you haven't checked Retro Phaze out yet, give it a look. It's awesome!
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