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#64101 - 21/08/2006 15:43 Temperature Rounding Rules
Roger Offline
Weather Freak

Registered: 31/01/2003
Posts: 698
Loc: Narooma
There were 5 centres in NSW that recorded a high of
27 on the 17/8/06.
The actual temps before rounding are as follows;

Bourke 27.8 rounded down to 27
Brewarrina 27.5 rounded down to 27
Camden AP 26.5 rounded up to 27
Narooma 26.5 rounded up to 27
Wanaaring 26.5 rounded up to 27

As you can see there is no consistancy as to rounding up temperature readings,should there be some rule set in place? Or should there be more honesty and give them out as is such is the case
with AWS's.?

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#64102 - 21/08/2006 15:46 Re: Temperature Rounding Rules
Blair Trewin Offline
Weatherzone Addict

Registered: 13/07/2001
Posts: 3699
Loc: Melbourne, Australia
Not sure what your source is - are you sure that the Bourke '27' wasn't a maximum from 0900 to 1500 only, with 27.8 being the 24-hour maximum.

The way it's supposed to work is that, where rounding is done, it is done to the nearest whole number. Values ending in .5 are rounded to the nearest odd number (so it is correct that 26.5 and 27.5 both go to 27).

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#64103 - 22/08/2006 10:13 Re: Temperature Rounding Rules
Roger Offline
Weather Freak

Registered: 31/01/2003
Posts: 698
Loc: Narooma
Blair, The source is the Synoptic list which showed
a max of 27 for the relevent locations.
I opened up each location to find the exact temperature.
Yes,it has been normal practice to round up when you
get to the halfway mark and round down if it is,e.g.
26.4 which becomes 26. But rounding down from 27.8
and 27.5 to 27 isn't the right way to go,don't you
agree?

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#64104 - 22/08/2006 10:23 Re: Temperature Rounding Rules
tomtankman Offline
Weather Freak

Registered: 01/05/2002
Posts: 147
Loc: Neutral Bay, Sydney
The temp in Bourke on the 18th reached only 27.1, hence the rounding to 27.

http://www.weatherzone.com.au/observations/dailySummaryHistory.jsp?wmo=94703

And here is an old thread regarding the rounding

http://www.weatherzone.com.au/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=1;t=005697#000000

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#64105 - 22/08/2006 14:44 Re: Temperature Rounding Rules
Roger Offline
Weather Freak

Registered: 31/01/2003
Posts: 698
Loc: Narooma
I stand to be corrected.

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#64106 - 22/08/2006 16:51 Re: Temperature Rounding Rules
Rob G Offline
Weather Freak

Registered: 31/07/2003
Posts: 673
Loc: Porters Retreat NSW
The common 3 rounding rules relating to figures ending in a 5 are:

(1) if the last significant figure is 5, truncate the 5 then add 1 to the figure
(2) if the last significant figure is 5, round to the nearest odd
(3) if the last significant figure is 5, round to the nearest even

Personally I apply the 1st rule, but in the scheme of life it doesn't matter. The latter 2 rules are generally preferred over the 1st because a temperature reading of 27.5, say, may come from a true temperature of 27.49, or 27.51. If you round all .5’s up, it will introduce a small upward bias because all true temps from 27.4500… to 27.4999… end up as 28 instead of 27. Odd/even rounding removes this bias. It appears the BOM apply the odd rounding rule. Brewarrina’s 27.5°C therefore becomes 27. With Bourke, it appears someone made a mistake, as the maximum was 27.1°C, not 27.8°C.

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