We had a nice soaking rain pass through overnight with about an inch of much needed rain for most of Mass. My Cocorahs gauge reported .99" this morning, while the Rainwise right next to it reported 1.05". These two gauges are usually within .01" of each other after a rain. 6% is a pretty big difference. Who do you think is over or under reporting?
If my gauges were only 6% different, I would tear down the goal posts in celebration! For example, in a single rain storm last week my VP2 recorded .32, Mr. CoCo had .39, and Mr. Rainwise had .36. All three collectors were reasonably close together. However, based on nearby reliable PWSs, I believe Mr. CoCo is probably the most accurate. Wind and gusts probably contributed to the differences in my recorded amounts. I used to "lose sleep" over such differences, but now I accept the differences as long as they are "directionally correct" (in my case, the three readings meet that description) and let it go at that. If the readings were .32, vs .67 vs. 1.40, that would be reason to be concerned because clearly something is wrong. What is a bit frustrating is both my VP2 and Rainwise "tippers" were made in 2016. But it goes to show you that the old fashion rain gauge, Mr. CoCo, is the tried and true reliable tool. No mechanisms or parts to go awry, just a plain and simple gauge (costing about $30) made from plastic!
Now I have done it! I have added more confusion to life. As noted above, I have three tools that have provided me rainfall measurements—a new VP2 ISS, a Rainwise 111 gauge and Mr. CoCo. To help determine the accuracy winner, I decided I would add a fourth tool—my 11 year old VP2 that I have upgraded with a new tipper mechanism (Davis part number 7852.804 Vantage Pro2 Rain Bucket Base and Bucket), SHT 31 and a thoroughly cleaned ISS (it sat in a bleach solution for 24 hours and it looks almost new)! Since I have two VP2 consoles, I can capture the VP2 ISS data (the new one and the refurbished one) separately—with a little help from Davis support (the console directions are horrible for doing this task, Davis walked me through the changes in less than 1 minute!) Unfortunately, I took two steps forward and three back. We had a modest rainfall today and the measurements follow: the new VP2--.25; the refurbished VP2--.34; the Rainwise--.29; and Mr. CoCo--.32. Each are reasonably close in proximity to each other at similar height above ground. Oh well, I am enjoying life with this hobby. Time will tell and additional rainfalls will be necessary, but I think the refurbished VP2 and Mr. CoCo are the apparent winners--at least today! I felt comfortable going to my new VP2 ISS (that uploads data to CWOP and WU) and manually "tipping" the rain bucket 9 times so CWOP and Weather Underground received what I believe are the "best" rainfall amounts.
Another winner are folks that own Davis equipment. The Davis telephone support is great, unfortunately the online support (e-mail) is slow to respond--but waiting on the phone for a few minutes and talking with a USA based support person is pretty unique and special. It makes you appreciate the Davis equipment and its higher cost. Brett Lane is the person in charge of Davis support--kudos to him and his team!