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0.01" vs. 0.3 mm Rain Gauge Bucket Tips

Discussion specific to Fine Offset and similar rebadged weather stations
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Buford T. Justice
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0.01" vs. 0.3 mm Rain Gauge Bucket Tips

Post by Buford T. Justice » Sun 30 Jun 2013 2:18 am

Does anyone know what the exact bucket tip amount is? It cannot be both.

If it is 0.01" per bucket tip, then that is 0.254 mm. Wouldn't that mean each bucket tip is short 0.046 mm for those measuring in millimeters?

If it is 0.3 mm per bucket tip, then that is 1/64 of an inch or 0.01181102362206". Wouldn't that mean each bucket tip is over 0.00181102362206" for those measuring in inches?

I went to Fine Offset's webpage and using this common model, it says:

1) "Rainfall data (inches or millimeters): 1-hour, 24-hour, one week, one month and total since last reset."

2) "Rain volume display: 0 - 9999mm (show OFL if outside range)

Resolution : 0.3mm (if rain volume < 1000mm)

1mm (if rain volume > 1000mm)"

So wouldn't that mean each bucket tip is 0.3 mm? If so, then those reporting in inches need to do an offset of 0.00181102362206" right?

Like John Harrison, I am obsessed with accuracy.

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Re: 0.01" vs. 0.3 mm Rain Gauge Bucket Tips

Post by steve » Sun 30 Jun 2013 8:21 am

A bucket tip is (nominally) 0.3mm. For people using inches, Cumulus converts the total for any given period by multiplying by 0.0393700787, which is effectively 0.01181102361 in per tip, and then rounding to 2 dp. No calibration setting is required.
Steve

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Re: 0.01" vs. 0.3 mm Rain Gauge Bucket Tips

Post by Buford T. Justice » Sun 30 Jun 2013 8:34 am

I have been slowly converting my logs over to metric values on a separate install of Cumulus. I fire up the other install so it gets imperial units 2-3 times a day. Anyway, I have been taking inches * 25.4 to get mm. Will my rain totals originally in inches be accurate rounded to the tenth?

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Re: 0.01" vs. 0.3 mm Rain Gauge Bucket Tips

Post by steve » Sun 30 Jun 2013 8:44 am

If I understand what you're doing correctly, you can't get back exactly to mm to 1 dp from inches to 2 dp. For example, 0.01 in is 0.254 mm, which rounds to 0.3 mm, but 0.02 in is 0.508 mm, which rounds to 0.5 mm rather than 0.6.
Steve

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Re: 0.01" vs. 0.3 mm Rain Gauge Bucket Tips

Post by mcrossley » Sun 30 Jun 2013 9:12 am

Maybe this would help - easy to convert to an Excel function.
http://support.microsoft.com/kb/155696

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Re: 0.01" vs. 0.3 mm Rain Gauge Bucket Tips

Post by mcrossley » Sun 30 Jun 2013 9:15 am

Actually Excel already has a function to do this MROUND()

You need the analysis pack enabled to use this function.

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Re: 0.01" vs. 0.3 mm Rain Gauge Bucket Tips

Post by Charlie » Sun 30 Jun 2013 9:56 am

Mark, the issue isn't rounding - it's un-rounding a previously rounded number and then multiplying to amplify the error even further.
I think you need the original tip count. You can calculate that as an intermediate step and use Excel to round to an integer, but it will be +/- 1 tip, which unfortunately doubles the original error tolerance.

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Re: 0.01" vs. 0.3 mm Rain Gauge Bucket Tips

Post by mcrossley » Sun 30 Jun 2013 10:14 am

Still think mround() will do it...

Code: Select all

mm	inches	mm	round(mm)	mround(mm,0.3)
0.0	0.00	0.0000 	0.0	0.0
0.3	0.01	7.6200 	0.3	0.3
0.6	0.02	15.2400	0.5	0.6
0.9	0.04	22.8600	1.0	0.9
1.2	0.05	30.4800	1.3	1.2
1.5	0.06	38.1000	1.5	1.5
1.8	0.07	45.7200	1.8	1.8
2.1	0.08	53.3400	2.0	2.1
2.4	0.09	60.9600	2.3	2.4
2.7	0.11	68.5800	2.8	2.7
3.0	0.12	76.2000	3.0	3.0
3.3	0.13	83.8200	3.3	3.3

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Buford T. Justice
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Re: 0.01" vs. 0.3 mm Rain Gauge Bucket Tips

Post by Buford T. Justice » Sun 30 Jun 2013 11:54 am

Let me see if I have this right. Each bucket tip is 0.3 mm and minutely bigger than 0.1" right?

I see MROUND is available in OpenOffice.org Calc so I might try this again with what I have done so far which is just the dayfile.txt and this month's log files.

Are wind run miles and mph values also calculated in a certain way from km? Fahrenheit and Celsius?

1 mile = 1.609344 kilometers
ºC = (ºF - 32) / 1.8

From:

1 kilometer = 0.621371192 miles
ºF = ºC * 1.8 + 32

If it is going to be a lot of work, maybe instead I will just start fresh in metric.
Last edited by Buford T. Justice on Sun 30 Jun 2013 2:06 pm, edited 1 time in total.

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Re: 0.01" vs. 0.3 mm Rain Gauge Bucket Tips

Post by steve » Sun 30 Jun 2013 12:22 pm

The station supplies wind speed in metres/second and temperature in degrees C. Cumulus converts as required.
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Re: 0.01" vs. 0.3 mm Rain Gauge Bucket Tips

Post by Buford T. Justice » Sun 30 Jun 2013 12:56 pm

steve wrote:The station supplies wind speed in metres/second and temperature in degrees C. Cumulus converts as required.
Using the formulas in my last post?

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Re: 0.01" vs. 0.3 mm Rain Gauge Bucket Tips

Post by steve » Sun 30 Jun 2013 1:08 pm

For temperature, it multiplies by 1.8 and adds 32. For wind speed, it converts from m/s to mph by multiplying by 2.23693629. Wind run is then calculated from the mph figure.
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Re: 0.01" vs. 0.3 mm Rain Gauge Bucket Tips

Post by Buford T. Justice » Sun 30 Jun 2013 1:26 pm

steve wrote:For temperature, it multiplies by 1.8 and adds 32. For wind speed, it converts from m/s to mph by multiplying by 2.23693629. Wind run is then calculated from the mph figure.
So to get the wind right, I would need to divide mph by 2.23693629 to get back to m/s then convert to km/s then multiply by 60 to get the correct km/h reading? There is no time conversion from m/s to mph then? Just the multiplication of the m/s reading to go directly to mph?

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Re: 0.01" vs. 0.3 mm Rain Gauge Bucket Tips

Post by steve » Sun 30 Jun 2013 1:40 pm

To convert from mph to kph directly, just multiply by 1.60934.
Steve

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Re: 0.01" vs. 0.3 mm Rain Gauge Bucket Tips & Metric Units

Post by Buford T. Justice » Sun 30 Jun 2013 3:36 pm

A few more questions which relate to the original subject and what I added on to it:

Does it matter what I have the Fine Offset display displaying? If the display is displaying °F, mph, and inches, does this affect Cumulus if it is set to °C, km/h, and mm or vice versa? Does the Fine Offset display actually use metric values, but simply converts them internally to imperial values if selected?

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