You've started measuring with the Pro and see that radon levels swing or change wildly up and down. Is this normal?
The short answer is yes.
Radon levels change
Not only can radon levels change drastically during a 48-hour measurement, but it is quite normal. Radon levels change rapidly for many reasons, and the change can be a factor of 5 within a single day.
The Pro is certified to be accurate enough for a 48-hour measurement, which is standards among home inspections. However, the reading per hour isn't that accurate. The Pro has an accuracy of 7% after 1 day of measuring (7% of measurements are within 1 standard deviation from the real radon level). However, on an hour to hour basis it is less accurate. This inherent uncertainty can also lead to additional swings in the graphs.
Another explanation is that someone is opening windows, doors, or changing the ventilation in some way during the measurement to try to corrupt the measurement.
Unfortunately, we cannot tell you which of these are to blame just by looking at the data. For an absolutely optimal radon level reading, we recommend measuring for 1 month or more.