add a ‘standard conditions’ sign

To add the standard conditions sign to enthalpy changes or electrode potentials I used to use an ordinary o crossed-out and superscripted:

However, I now use the symbol ϴ as a superscript. It’s too big so I make it font size 8 then raise it by 3 points. I wouldn’t want to do that every time I need a standard sign so it’s quicker to use the macro here.