On March 11, 2011, a catastrophic earthquake and tsunami struck Japan, killing at least 9,000 people. The twin disasters damaged the Fukushima Daiichi nuclear power plant, knocking out power to its cooling systems and raised radiation fears in the country. Tokyo, located 250 km southwest of the reactors, had one reported reading of 0.809 microSievert (1000000 microSievert equals one Sievert) at 10-11 a.m. local time on March 15. What does that measurement mean in comparison to what we get on a normal basis? Here's a look at other exposure levels: