Topic: Imperial to Metric and Back

[jammer13]

This is a basic question, but I didn't see much discussion on the forum about this.  I just started using MB to upload to WU from my VP2.  The VP2 transmits in English/Imperial units but I am taking it that the MB converts to metric and then back to English for WU.   For example, WU now shows wind at 1mph from the VP2 as 0.9mph.  I assume that's because it's converted to m/s with one decimal point precision and then converted back again to WU. This is not a significant problem but just checking my understanding.  There is no way to use English as default basis as far as I can tell.

I'm sort of inferring this from the fact that Weather Display shows the same rounding issue and I have it retrieving data from MB using the XML live Data feature and the wiki documents the format of the output (eg wind is m/s at one decimal point).

[chief-david]

WU does a lot of rounding. Even for imperial values. Especially wind. I don't think I have seen WU put any wind value in decimals.

[Jáchym]

Based on this:
http://wiki.wunderground.com/index.php/PWS_-_Upload_Protocol

WU seems to accept wind in mph, so MB probably sends it in mph, which then does not make much sense, it must be some rounding on the WU side

[chief-david]

Does it really matter if it is 17.1 or 17?
Same with temp  Who cares if it is 40 or 40.2 on any scale.

[Jstx]

FYI:
Just for reference, I found this link to a useful conversion page somewhere (maybe even from somebody here?).

Weather Conversion Calculators 
These calculators were developed by the 28th Operational Weather Squadron

http://craigsweb.net/mystuff/wxcalculator.htm

[Jáchym]

Very interesting link John, thanks for sharing

[jammer13]

FYI:
Just for reference, I found this link to a useful conversion page somewhere (maybe even from somebody here?).

Weather Conversion Calculators 
These calculators were developed by the 28th Operational Weather Squadron

http://craigsweb.net/mystuff/wxcalculator.htm

Yes I had done it by hand and here's what I think is happening.

VP2 reading =1.0 mph =0.447 m/s but MB rounds to one decimal so it stores it as 0.4 m/s.  Then MB likely reconverts to mph for WU so 0.4 m/s = .895 mph which is rounded to 0.9 mph by either MB or WU.  You can use this calculator to do the same.

If MB used two decimals for wind then 0.45 m/s = 1.0 mph and the output would equal the input (starting value from VP2).

Does it really matter if it is 17.1 or 17?
Same with temp  Who cares if it is 40 or 40.2 on any scale.

Agree with this. MB is a fantastic utility. It was mostly an academic question, but it shows trade-offs developers have to make.  I'm thinking that maybe the lower level of precision was used to limit the storage space since RAM is at a premium. 

[Jstx]

Glad y'all liked the calc link. If it could be 'stuck' somewhere around here for reference, go ahead somebody.

BTW, there is a fantastic, global first-in-class calculation reference website called "Martindale's" or somesuch (IIRC, don't have the link at hand).
It has tens of thousands of calculation links available, in every field imaginable; a veritable Wiki for calcnuts.
I'll try and look it up and edit this post w/the link(s). I've always found it extremely useful, and have used it since the 1990's.

[Jstx]

Glad y'all liked the calc link. If it could be 'stuck' somewhere around here for reference, go ahead somebody.

BTW, there is a fantastic, global first-in-class calculation reference website called "Martindale's" or somesuch (IIRC, don't have the link at hand).
It has tens of thousands of calculation links available, in every field imaginable; a veritable Wiki for calcnuts.
I'll try and look it up and edit this post w/the link(s). I've always found it extremely useful, factual and reality-based    , and have used it since the 1990's.

Found that Martindales link. Absolutely the most comprehensive resource of it's kind I've ever seen (and I've used it since the early innartoobz days).
It has a whole section on WX.:

MARTINDALE'S

CALCULATORS ON-LINE CENTER

(Calculators, Applets, Spreadsheets, and where Applicable includes:
Courses, Lectures, Manuals, Handbooks, Textbooks, Simulations, Animations, Videos, Movies, etc.)

http://www.martindalecenter.com/Calculators.html

WX:
http://www.martindalecenter.com/CalculatorsD_Wea.html

Even the dreaded Climatology & Physics of Climate (ruh-oh):
http://www.martindalecenter.com/CalculatorsD_Wea.html#MET-CLIMATOLOGY