The prefix is sometimes applied in non-standard ways:
one megaton (a unit often used in measuring the power of nuclear weapons) is 1,000,000 tons. The metric tonne is 1,000 kg, so it is in fact this unit that should be called the megagram.
in computing, a megabyte is 1,048,576 (220) bytes. The prefix mebi has been suggested as an alternative.
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