I got one for Christmas last year and just took it out of the box to install batteries and set outdoors. The innards have a "see-saw" type of device that collects the rainwater and self empties. This seems to be purely mechanical in nature and I cannot see how it measures anything. Also the battery housing is in there but the 2 do not seem to be connected to each other in any way. For the life of me I cannot see how this thing will measure rainfall but the other day we had a trace amount overnight and there it was on my indoor device showing .02" of rain!