The great difficulty in giving directions in cookery-books, and in understanding them when given, is the insuperable one of avoiding vague expressions.

For instance, suppose we read, "Take two onions, one carrot, one turnip, and one head of celery,"-- what does this mean?
It will be found practically that these directions vary considerably according to the neighbourhood or part of the country in which we live.

For instance, so much depends upon where we take our head of celery from.

Suppose we bought our head of celery in Bond Street or the Central Arcade in Covent Garden Market on the one hand, or off a barrow in the Mile End Road on the other.
Again, onions vary so much in size that we cannot draw any hard-and-fast line between a little pickling onion no bigger than a marble and a Spanish onion as big as a baby's head.

It would be possible to be very precise and say, "Take so many ounces of celery, or so many pounds of carrot, but practically we cannot turn the kitchen into a chemist's shop.