PortaTree Weather Deluxe Hardware - Manual (Page 18)

restart the program for the change to take effect.
A word about files and data
The PC Weather Center software opens all files and closes them immediately.
This means that other programs, such as data base managers or spreadsheets,
can access the data, as long as you remember that the PC Weather Center will be
using the files, they are safe to read. Also, this allows different parts of the PC
Weather Center software to run while other parts are active, like weather logging.
But care needs to be taken to prevent a 'collision'.
If the weather screen is logging weather, and you open the current weather data,
then save it, any weather data 'logged' in the interim could get overwritten. Also, if
you enter a time slip from the weather screen, you should NOT have the race
data screen open and running with data.