Would it have anything to do with the math precision in converting to inches, combined with packet loss? While I've been keeping track (a few months or so) of the rain values in a given reading, it appears to be recording in hundredths of an inch, but converted to mm. (0.254mm = 0.01 inches) Here's all of the distinct values I've received. (these are divided by 1000 since the actual packet contains no decimal)
0.2540
0.5080
0.7620
1.0160
1.2700
1.5240
I get an average of 84 rain packets per hour. But even in the last 24 hours, that range has been from a low of 79/hr to 95/hr. We haven't had any rain, so I'm guessing the variability is packet loss.