Better make sure that milkshake is half milk, Kim. (Jumanael Heloleh - Reuters)

It's one thing to declare large sugary drinks as contraband, which New York mayor Mike Bloomberg infamously did late last year.

It's quite another to actually write the rules and regulations that determine what counts as a large sugary drink. That's where the regulators have to come in — and, down to the teaspoon and calorie, determine how to define the word "sugary."

The New York ban on sugary drinks larger than 16 ounces takes effect next Tuesday. With it comes a new fact sheet for restaurant workers, explaining how best to hew to the spirit of the law.

First, you've got to know if a drink has sugar in it altogether — and, chances are, the menu label won't necessarily even say "sugar." There are 11 sweeteners that New York City identifies as sweeteners with calories:

This means that a milk drink, with many calories, could still be served in a size larger than 16 ounces (but, as the regulations stipulate, a milkshake must be least half "milk,  ice cream or other milk substitute.").

Then, you have to figure out if the beverage in question is sweet enough to trigger the new regulation. The law standardizes a "sweet" beverage as one with more than 3.125 calories per ounce. That's relatively easy to sort out if you're selling a standardized beverage, like Coca Cola. But what if you're mixing up coffee drinks at Starbucks? Or serving homemade lemonade?

Those drinks are also subject to the new rule. If a Starbucks customer orders a grande beverage, it would be 16 ounces, and can have as much sugar as desired. But if they go the next size up to a 20-ounce Venti, than the barista is instructed to add only three tablespoons of sugar, so as to stay under the 3.125 calorie per ounce limit.

The new regulations underscore the challenge of operationalizing a seemingly simple, one-sentence public-health policy. It's so complex that, as The New York Times reports, Dunkin Donuts has started handing out flyers to prepare their customers for the changes.