Wunderground posts a number called “Hourly Precipitation”, which seems to indicate that it would use the number under “rain rate” on Weather display. However, I am pretty sure that Weather display sends it the amount of rain since the last report (e.g. .04 inches in the last 5 minutes rather than .48 inches per hour). I verified this by the following experiment. There are four weather stations reporting in my area. Two (including mine) use your software. In both of these cases, the sum of the Hourly Precipitaion numbers (retreived via the Comma Delimited method), added up to exactly the daily precipitation reported. This was not the case for the other two, which used different software.
its a can of worms
originaly WU was intended and setup for hourly uploads
i then set WD to report the rain by the method because people wanted that
now, in recent verisons, it reports the total rain for the day since the last reset, and WU can deduce from that the rain in the last hour