Ever since the Fukushima No. 1 nuclear power plant began spewing radiation on March 11, many have struggled to understand the unfamiliar units used to measure it.

A few days after the quake and tsunami damaged the reactors and cut lifelines in the disaster zone, news spread that radiation levels in the air had climbed sharply across Fukushima Prefecture, and the words "microsievert" and "millisievert" began to enter the popular lexicon. One millisievert equals 1,000 microsieverts.

Soon reports emerged that the government had placed a ban on spinach and other green vegetables as well as milk produced near the nuclear power plant because radiation levels exceeded allowable limits. Suddenly, another term — "becquerels" — was sprung on the public.