I have this wonderful recipe book: it's an old WI one and the recipes have been sent in by WI members.
But they're so funny! There's 1 thing that I make out of it-chocolate mint cakes. It's a biscuit base with minty butter icing and a chocolate top.
But the recipe says:
1 packet of rich tea biscuits....
So, how many biscuits or grams of biscuits do I need? The base takes 4oz of margarine. Obviously I am using butter. 
Next time I'm going to write notes on the recipe about quantities!