Focus Question: What are SI units, and why are they used?
In 1999, NASA lost the Mars Climate Orbiter because one team used English units
(inches, feet, and pounds) while the other used metric units for a key spacecraft
operation. That was a $125 million dollar mistake... oops! Distance can be measured in
inches, feet, yards, miles, or meters. So, how do scientists know which to use?
Since there are different ways to measure things, scientists and engineers use the
International System of Units, known as Sl units, in order to stay on the same page. This
is important whether you are measuring speed, distance, temperature, or anything else!
To avoid confusion, always show what units of measurement you are using.
.

a system of physical units ( SI units ) based on the metre, kilogram, second, ampere, kelvin, candela, and mole, together with a set of prefixes to indicate multiplication or division by a power of ten.

Explanation:

The problem here was not the error; it was the failure of NASA's systems engineering, and the checks and balances in our processes, to detect the error. That's why we lost the spacecraft.

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