You've started measuring with the Pro and the radon levels swing or change wildly. Is this normal?
The short answer is yes.
Radon levels change
Not only can radon levels change drastically during a 48-hours measurement, but it is quite normal. Radon levels change rapidly for many reasons. Just the stack effect alone often naturally changes the concentration by a factor of 2 within a single day.
External factors and tampering alerts
Another explanation is that someone is opening windows, doors, or changing the ventilation in some way during the measurement to try to corrupt the data.
External factors such as the weather can also greatly influence the radon concentration. Make sure you review the weather history when analyzing a suspicious measurement.
If the Corentium Pro has been moved during the test, you'll see an Event or a Tampering Alert. For more in-depth information on the alert, you will need to use the CRA desktop software and review the excel data in conjunction with the graph.