Aw...thanks! I dug out my dad's slide rule (we're talking 1940's), trying to follow her logic. However my scale omits the C designation, so I can only guess if I'm following it correctly. I wish she had given a few recipe values to see if I was using it correctly. I tend to use my proportion scale (a leftover from art school) more often than not...or simply basic algebra: If 2 eggs uses 3 cups of flour, then 3 eggs > x?. Solve for x.
When I'm really lazy, I make a spreadsheet and copy the scaling proportion to a new column. I did this for my family's wedding desserts and cookie tables.. when I was increasing desserts 10 to 15 fold.