I must say it's a great improvement with the stats

I have a four questions today:
*What triggers a rainy day?
ie my stats for May this year shows 1 rainy day in stats. The 16th of may I had 1.4mm and the 29th I had 1mm. Here is the graph: http://vindkast.no/wx_graphweather.php? ... 8&delta=31
And my stats:
http://vindkast.no/MyGWStats.php?&month ... 008_05.xml
*What could be the reason for Tn showing NA in the stats?
*I have a solar sensor and counts sunshine hrs. (A cumulative seconds database) Is it possible to get GW to calculate hrs of sunshine for the periods? ie $cumul[solar_time]/3600seconds=hrs of sunhine?
*Last Question. Is it possible to plot solar radiation on a logarithmic scale?
regards
Audun
http://vindkast.no