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Tennis uses the imperial system of scoring
(programming.dev)
Sometimes we have those little epiphanies in the shower.. sometimes they come from other places. This is a home for those epiphanies.
Isn't it only when they're tied at 40, at which point it's deuce and then advantage to whichever side is at game point. Whenever they're tied anywhere else like 15-15, don't they say 15 all.
Disclaimer my knowledge of tennis is pretty much limited to Mario Tennis games and Wii Sports