It is very important to baseline any activity and have a common understanding.
One of the typical complaints that we read about while purchasing external HDDs online are about the size. Most conplaints are about the fact that a 1 TB HDD is reporting a size of 900GB only. This infuriates many people.
But, an important fact needs to be noted. While computer manufacturers and OS vendors typically count 1K to be 1024 bytes, HDD makers count 1K to be 1000 bytes only. Then for each K, there is a 24 byte difference, which adds up when the volume of the storage increases.
A similar problem occurred in a famous flying incident, which came to be known as the ‘Gimli Glider’. In this case, a 767 flying in Canada ran out of fuel mid-air. While a mishap was avoided as the pilots managed to make the aeroplane glide and finally land on an abandoned airfield, later investigations revealed the root cause.
The root cause was measurements. In the normal scheme of things, fuel was loaded into the aeroplane using KiloLitres (as per the new metric system introduced at that time). But, when fuel was loaded in Europe, it was being measured in Pounds (as per the old system). While the numbers matched, the result was that the aeroplane was only half-full.