Until you start looking at old stuff and have you figure out if they were working with the "millions scheme" or "thousands scheme," and if "1 billion" is equal to 1012 or 109
99% of it is metric. I think the biggest outlier is home care, where you go visit some grandma who's actively offended by metric, so if you tell her to take 7.5mL of something she'll just do the deer in the headlights thing, then shove the bottle up her ass.
Tell her instead that she needs to take 3 Mountain Dew caps full and suddenly she can follow instructions enough to not kill herself.
I know it should be obvious and maybe I missed the sarcasm, but the teaspoon unit is in no way the same as an actual teaspoon utensil. I also don't use my own feet to measure length.