It is number rounding by VWS, it does not record an actual .04 on each bucket tip, but something like .0385 (not sure on the exact number). But the VWS displays rounds that up to .04 Eventually these "rounding errors" catch up so when you multiply the actual number of .0385 x 8 Bucket tips you get .308. Then VWS rounds that number as well and you end up with .31. So we all see it, if you change the precision of the Broadcast.jpg to more places you will see the actual number but then who wants to look at rain number to 8 places.