I'm just starting to dabble in Indian cooking and have noticed that recipes call for certain quantities of ground spice. I also understand that it's preferable to grind spices as needed. How do you know how much of a given whole spice will yield the desired amount of ground spice (eg. how much coriander or cumin seeds do you grind for, say, 1 tsp. of ground spice)? Is there a formula? Thanks. Btw, I'm using Julie Sahni's Classic Indian Cooking. Thanks!