I am using Rad 7 H2O (Durridge). Actually, I have get the radon concentration data using via Rad7 instrument, now i want background concentration of radon ?
You can calculate mean of all the data, then trim 1% of extreme values and recalculate mean. After that trim 2% of extreme values and recalculate, then 3% and so on, to plot Trimmed mean vs % of data trimmed. Mean goes on reducing and after some point it stabilizes, the stable value is background.