A residence floormate I knew back in university also worked as a bartender at a hotel.

His one story relevant to this thread is he once poured a drink for a customer over ice without measuring it. Think scotch or whiskey. Customer said there’s no way that’s an ounce. They argued for a bit; my friend poured everything from the glass into a shot glass minus the ice, and it was exactly on the line. End of argument.

He admitted to me that some of that may have been water from the melted ice.