#64101  21/08/2006 15:43
Temperature Rounding Rules

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

Weatherzone Addict
Registered: 13/07/2001
Posts: 3835
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 24hour 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

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

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/cgibin/ultimatebb.cgi?ubb=get_topic;f=1;t=005697#000000

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#64105  22/08/2006 14:44
Re: Temperature Rounding Rules

Weather Freak
Registered: 31/01/2003
Posts: 698
Loc: Narooma


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#64106  22/08/2006 16:51
Re: Temperature Rounding Rules

Weather Freak
Registered: 31/07/2003
Posts: 750
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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