For instance when buying fuel in US Gallons and then converting to Litres/KG and Pounds it is all too easy to get the digit in the wrong place.
Hence the Gimli Glider. Air Canada 767 en route to the West ran out of fuel and landed dead stick on the disused Gimli runway. ( near Winnipeg )
If he makes any calculation using a calculator..........
Have mentioned before - carry a key ring sized navigation computer in my wallet, using it at the supermarket one day, the "work experience" teenager asked me what it was? A circular slide rule, I replied. "What's a Slide Rule" ? was his reply. One could weep.