Was going to post a link demonstrating that, but that site has been down the past few hours.
When workers go into a radiation area, they carry at least 2 types of personal dosimetry. One kind can be read by the individual while being exposed, one has to be read by a machine after the exposure. In addition, the areas around the site are routinely surveyed and radiation levels are posted in the area and briefed before personnel enter the area for work. This aids in determining an individual's exposure by counting up the amount of time spent in a given radiation area. By reviewing and comparing all three methods, a pretty accurate exposure level can be determined.
Radiation monitors can not be used unless they are in current calibration--calibrations are done periodically depending on the type of detector, and standard procedure is to check a detector's calibration before using it. Some detectors even come equipped with their own radioactive source, so calibration can be checked every time the instrument is used. BTW, rad monitors don't estimate anything...they show actual rad levels, as long as they are correctly calibrated.
TEPCO and the Japanese government couldn't lie about rad levels if they wanted to--too much independent verification there for them to get away with it. There may be some discrepancies, but I give them the benefit of the doubt.
The people working at Fukushima are all very well trained in all aspects of radiological controls. They are smart, competent, and capable. They, above all, know the risks they are taking. Same goes for anyone who comes in from outside Japan to help in the recovery and cleanup. I would have absolutely no problem going there to work, if I was not otherwise busy (my bad knee wouldn't help, either).
BTW...a few zoomies now and again are good for the soul...};o)