Why the name 'Two Cups'

My grandmother was a shearer’s cook and she could whip up 3 or 4 sponge cakes for morning tea while chatting to you over coffee. She didn't ever follow a recipe and rarely wrote one down, everything was done by memory, taste, texture, smell and of course, amazing intuition.
 
My aunt asked her for recipe and in it was "a cup of flour" and "a cup of sugar". For a year she tried and couldn't make this recipe work.
 
So one day she was chatting to my grandmother and my grandmother couldn't figure out what was wrong either. It was when she reached up and got two very different sized tea cups from the top of the cupboard that the penny dropped. There is one large cup for flour and a small cup for sugar.
 
It always reminds me that one cup isn't always the same as “Two Cups”