The term "proof" dates back to 16th century England, when spirits were taxed at different rates depending on their alcohol content. Similar terminology and methodology spread to other nations as spirit distillation, and taxation, became common. In England spirits were originally tested with a basic "burn-or-no-burn" test, in which alcohol that would ignite was said to be "above proof" and alcohol which would not was said to be "under proof". The breakpoint between under and over proof was defined as 100 and was the basis for taxation. Because alcohol's flammability is highly dependent on temperature, 100 proof defined this way could range anywhere from 40 to 90% ABV in normal air temperatures; at 100 proof would be 60% ABV.