Official source to show that SF calcs are legit?

We all know that it’s standard practice in New York to measure the square footage of an apartment from the center line of demising walls to the outside of exterior walls. That’s just how it’s done, even though there’s no legal standard, and even if it seems a little deceptive to people getting involved with real estate for the first time. My question is, if you were trying to reassure a skeptical buyer that all square footages are measured that way in New York, is there any authority you could show them to confirm this? I’m thinking maybe the AG or the Department of Consumer Affairs – even an industry group like REBNY. Do any of them publish unofficial official rules on measuring the square footage of an apartment?