I'll admit, I'm old and my learning (through bartender's school, no less) reflects that. Most shot glasses will hold a jigger, but you don't fill it for a shot. Further down the page you linked, under "jigger," shows a tool we use(d). A "shot" was a drink, the "measure" was a jigger (1.5 oz) or a shot (1.0 oz). In programming terms, the word "shot" was overloaded.
