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Wikipedia defines the Scoville Scale
“the measurement of the pungency (spicy heat) of chili peppers or other spicy foods as reported in Scoville heat units (SHU), a function of capsaicin concentration. The scale is named after its creator, American pharmacist Wilbur Scoville. His method, devised in 1912, is known as the Scoville Organoleptic Test.
Unlike methods based on high-performance liquid chromatography, the Scoville scale is an empirical measurement dependent on the capsaicin sensitivity of testers and so is not a precise or accurate method to measure capsaicinoid concentration.” The Scoville Scale is the only true way to measure hot sauces.
Got it? No? That’s why there’s a diagram… See below.