On the subject of units - I am a PPL but like to keep a "watching" brief on the commercial forums (fora?).
Is it just history that the units in aviation are such a mix? as examples:
Altimeter settings in hectopascals (aka millibars) or inches of Hg
Altitude (in most place) in feet
Runway lengths in feet or metres
Distances in nautical miles
On light aircraft I have flown I have come acoss the following mixes of units :-
Fuel capacity in US gallons, litres, imperial gallons, kilos or pounds
Weight & balance in lbs and inch pounds, kilos and kilo cms
Air speeds in Knots, mph or Km/hour
Tyre pressures in lb/sq in or bar
Oil capacities in litres, US quarts, imperial pints
Boost in inches (of Hg?)
I know that a lot of these are "inherited" from the country of manufacture of the aircraft , but for safety and ease of use I have always been surprised that there is no standardisation.
It is just too easy to cock up a weight & balance calculation because of mixed units.