The 1-day average value is the average value of Radon over the past 24 hours. It is a moving average, in the sense that whenever a new sample is added to this average, the oldest sample is then discarded. So after 3 days, you still read 1-day because that value is the average value of the past 24 hours.

The weekly average works in the same way: every day, a new daily average value is added to this reading, while the data from the oldest day is then discarded. The weekly average value appears after you measure for at least one week.

The only reading that contains every single sampling ever made since the current measurement started is the long-term average value, which is the most important reading on your machine.