Problems with script

So I was trying to write a macro to calculate how close I am to uncrushable, when I ran into a problem. I narrowed it down to this part not returning anything.

/script DEFAULT_CHAT_FRAME:AddMessage(GetCombatRating(CR_DEFENSE_SKILL))

What am I doing wrong here?

IIRC the script command doesn’t work at all in Classic.

I believe it’s due to the modern API they are using for Classic.

This seems accurate–none of my Devilsaur tagging scripts are working either.

The script command is working fine for other stuff, or for the rest of the calculation if I pull the GetCombatRating out. the struggle I"m having is with the GetCombatRating