Order of magnitude

Knowing whether a number is in the hundreds, the thousands or the lakhs, before caring about its digits.

Most analytical errors are order-of-magnitude errors rather than precision errors: a crore mistaken for a lakh, a million for a billion, a monthly figure annualised twice.

The habit that catches them is to state the expected magnitude aloud before computing, and to check units at every step. Indian and international numbering conventions collide constantly, and the crore-to-million conversion is where it usually happens.

Get the size right first. Precision afterwards.