I absolutely love Chernobyl (2019) and have watched it many times. But there is still one scene that I don't fully understand.
In Episode 2, "Please Remain Calm", while trying to figure out where the previously detected radiation is coming from, Ulana Khomyuk calls the nuclear power plant in Ignalina. After a short exchange, she hangs up the phone and states: "They're at four. It's not them."
What does that mean? Is "being at four" a common expression that I don't know about? Or are the subtitles at fault here (I checked the ones from the retail Blu-Ray)?