The gill is still a legal measure and FWIW it is illegal to sell overmeasure in English (and Welsh) pubs because of the drink drive laws. Dunno about Scotland. When I worked at W&T Avery we discussed weighing beer at the pump a means of dispensing correct measure and gave-up because of having to measure temperature and calculating (without embedded chips at the time). But it would have solved the "pint with or without froth" argument. If you can prove the froth makes the measure up to one pint there is no argument. If you can't the liquid has to reach the measuring line.

Breweries have forgotten the legal battles that have ensued over the years on three occasions in my lifetime. Anyone brave enough to argue with the landlord? With cider some just serve short measure and dare you to say anything.