Mom's "Modern Carpentry" book

So, browsing through Mom's 1976 version of Modern Carpentry and I ran across this...

What a great little memo! It looks like her handwriting to my dad. I wonder what stage of the house build they were in and what the circumstances were. I kinda picture her sitting at the kitchen table, pouring over measurements and plans and my dad talking on the phone as he walks by to get a snack. Maybe she flags him down on his way back to the living room and jots this note so she can get feedback on a decision that's to be made.

Fun to imagine them collabrating on the project.