Measure of apparent "heat" for hot peppers

The Scoville Heat Unit measures the spiciness of chiles / peppers, based on the capsaicin present. (This is the chemical that stimulates pain in nerve endings; i.e. "heat", in your mouth.) The Scoville measure was devised in 1912, and involves dilution with sugar in solution until the pepper cannot be tasted. Accordingly, the Scoville rating is somewhat subjective.

Some common peppers and their rating:
0   5000          20000                 70000           300000
+----+----+----+----+----+----+-- / -+----+----+----+- / -+
                    --------Hot-- / --
                                     ----Extremely Hot / --
With information from