Don't worry, as I pilot I have been exposed to all sorts.
Just as one example, fuel can be measured in US gallons, real gallons, litres, pounds, or kilograms. Several of these units are involved in a typical flight. Refuelling, W&B and performance are perfectly likely to need to be calculated in three different units.
Get the conversion wrong and you can be overweight or, usually worse, run out of fuel.
And yes, this has happened to airliners, not just amateur pilots in spamcans.
