The numbers indicate the radiation levels in Fukushima prefecture where nuclear power plant is situated.
The top row indicates when it was measured starting from June, over the past 6 years. It has been measured across the 19 spots which appeared in the left columns. The unit is micro sievert per hour. It tells you the intensity level.
For example, if you take an X-ray CT scan, you will be exposed to 7-20 micro sievert of radiations. Or if you take round trip flights from Tokio to New York, you will get exposed to 0.2 micro sievert of radiations. More than anything, we all exposed to 1.26 micro sievert of radiations from the air annually. We need to clarify the point that if we are taking about the intensity level of radiation or exposure dosage in certain amount of time when we talk about this topic.
The bottom row highlighted in green indicates the average across the 19 areas.
The data says the intensity level of radiation in Fukushima has dropped 84 % over the 6 years. This is just a data. As far as I know, the only newspaper, FUKUSHIMA MINYU wrote about it on April 27th, 2017. I thought I just needed to write it up here.