Mine arrived yesterday and luckily got it up prior to a good storm.
I noticed the rain measured was .07" lower than two other rain gauges I have. The others measured .29" and the Atlas measured .22"
I did not see instructions on adjusting the rain gauge.
I was also wondering what is the +/- norms in rain measurement? I would think just a few big drops/gusts would cause some variations. .07" of rain is not a lot.
Mine were lower on my only rain event too, similar to your readings. I attribute my lower readings to an unlevel unit. I noticed I didnt have my unit mounted properly to the pole, and fixed that. So, Im now hoping to have a leveled unit and proper rain readings.