Rain Reporting

I am a bit confused. I created a log file from an INF file
Imported the TXT file into EXCEL
I selected my dates and filtered on them.
The column that says ‘rainlastmin’ shows a value of 0.5. What does this actually mean??
Between 19:00 and 23:00 it was 0.5 in the rainlastmin column!!!
Dailyrain shows zero as does monthly and yearly columns!??

Help!!