How to measure a lobster or size an egg [Basicmetrology]

There are measurements in daily life where only certain points along a continuum need to be precisely known. Purchasing the least-expensive postage stamp for a letter has been a traditional example. In France (where I live), I can save a little money if I can be sure that my letter weighs less than 20 g. The post office does not care to know how much under 20 g. This type of less-than/greater-than measurement also turns out to be important when catching lobsters or selling hen eggs.