I have been using the VP2 metric rain gauge for about 8 years, but now I have bought an inch.
What is the difference between measuring the accuracy of these two quantities, does anyone know? #-o
If you’re old rain gauge is not working any more you can simply swap the weight on the bottom of the tipping buckets from your old one on to the new. This will convert it from 0.01" to 0.2mm per tip.
The instructions are on pages 14 & 15 of the ISS manual, which you can download from the Davis website if you don’t have it handy. 
Yes, but the question is which one is more accurate, whether 0.2 mm or 0.01 inch
Well 0.01" = 0.254mm so the metric has slightly greater resolution, but arguably - all things being equal, which they probably will not be - they should have the same accuracy.
Don’t confuse resolution with accuracy, there are probably other factors that swamp the difference between inch and mm gauges.
The smaller the bucket, records more accurate rain tips, albeit only a little between 0.2 mm and the 0.1 inch" which equals to 0.25 mm.
With 0.20 - 0.24 mm and then 24 hours without rain, the metric bucket will record 1 tip of rain. The 0.1 inch bucket will not report any rain
With 0.40 - 0.49 mm and then 24 hours without rain, the metric bucket will record 2 tips of rain. The 0.1 inch bucket will report 1 tip of rain
Wim
Thanks for your feedback.
I use WLL to download data to WD but the rain reads in inches via UDP.
That’s why I also bought an inch rain gauge.
Being in the US, I never thought too much about the difference in the Davis Rain collector when I ordered my station a few months ago. Wim is correct. If you take one inch of rain as equal to 25.4 millimetres, then you get the following RESOLUTION(not accuracy)…
1" rain = 100 bucket tips at 0.01" per tip.
25.4mm rain = 127 bucket tips at 0.2mm per tip.
for the 27% increase in resolution, I may convert mine to metric, and let WD convert it back to inches. If I do that, will it cause me any problems, and what else would I need to change?
In that case, I don’t understand why there are 2 types of rain gauge, why they didn’t produce only one type.
I found out how much water is needed to flip the inch collector, and it showed me 5.6mll of water, while the metric collector should be set to 4.28mll of water.
Because people like to see the rainfall increment in regular round units rather than irregular steps (after conversion and rounding) with odd numbers of decimals.
I’ve noticed that Davis sells some of his station models with a weatherlink live instead of a console.
So far there is a small selection, but I think that there will be more versions of those versions when the user will be able to choose whether he wants a station with a console or with a wll.
If the user wants to send data to the cloud and use wd at the same time, it is necessary to have an inch collector because wll only reads collisions in inches and not in metrics. This is my case and that’s why I bought an inch collector.
I don’t know if I did well or not.
Following on from my previous post, if you had a metric gauge and imperial units, then you would see this…
Tip mm inch
1 0.2 0.01
2 0.4 0.02
3 0.6 0.02
4 0.8 0.03
5 1.0 0.04
6 1.2 0.05
7 1.4 0.06
8 1.6 0.06
9 1.8 0.07
10 2.0 0.08
11 2.2 0.09
12 2.4 0.09
13 2.6 0.10
So unless you were prepared to use more than two dp’s then you would not “see” any extra resolution.
Tip mm inch
1 0.2 0.008
2 0.4 0.016
3 0.6 0.024
4 0.8 0.031
5 1.0 0.039
6 1.2 0.047
7 1.4 0.055
8 1.6 0.063
9 1.8 0.071
10 2.0 0.079
11 2.2 0.087
12 2.4 0.094
13 2.6 0.102
But if you have an imperial gauge like Matrix and you display metric in WD you will get:
Tip inch mm
1 0.01 0.3
2 0.02 0.5
3 0.03 0.8
4 0.04 1.0
5 0.05 1.3
6 0.06 1.5
etc.
because WD only displays 1 d.p. for mm.
And you will only get that if the rain rate is high. Quite often you will get 0.3, 0.6 and then maybe 0.8 and 1.1; and the total rain for the day/month/year saved by WD may not quite agree with the daily numbers you saw displayed. . .
But who worries about a tenth of a millimeter here or there, no tipping-bucket rain gauge is that accurate.
P.S. my modified rain gauge has 0.25 mm tip, as near as dammit to 0.01 inch.
Yes, that’s exactly how it works, 0.3 0.5 0.8 1.0 etc.
I think I bought well.
The question is really moot anyway. The vp2 rain gauge is not really all that accurate, it may be off by as much as 10 percent depending on rain rate, wind etc. To be truly accurate you must use a standard rain gauge set on a pole just touching the ground. and empty it every six hours at 00, 06, 12 and 18Z. The vp2 is plenty accurate enough for us amateurs.
Rick