Surely in this day and age
Well that is the nail on the head! The aeroplane was designed and built half a century ago!
On calibrating the 'generic' fuel Hawk.
Takes about an hour on the outside. Start with empty tanks and fill them up with a known quantity at the time (I used 5 USG) then dipstick it after each fuel addition and put it on the graph that comes with it.
Repeat for each tank and you have your own calibrated graph. Works well.
If you buy the pre-calibrated aeroplane specific one make sure it is the right one for your aeroplane. Tanks do differ from one variant to the next.