Peter, I understand your concern, and I share it. It's as bad a "juice of half a (lime, lemon, whatever)". But what can be done? It's easy to specify a volume of juice, but what could be done about leaves? And what about the variability of muddling technique? I don't see a solution. For me, I sometimes make dated notes on the recipe, just as I do when 'tuning' someone else's recipe to my (or my wife's!) tastes. Sometimes the outcome is multiple variations. In my case, that would include margaritas and daiquiris.