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Old 2015-09-06, 02:27   #1
Xyzzy's Avatar
Aug 2002

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Default Annoying Ambient Air Anomaly Analyzed and Answered!

We are posting this in Miscellaneous Math because it is a very trivial thing, but it stumped us for a very long time!

We ride our motorcycle many hours a week. It has an ambient air temperature display, which is pretty convenient. But, it only displays certain values. For some reason it skips some numbers as the temperature goes up or down.

We wondered about this for far too long (Weeks!) until we came across an answer to this vexing dilemma.

The (°F) numbers we have seen are: 77, 78, 80, 82, 84, 86, 87, 89, 91, 93, 95, 96, 98, 100, 102, 104, 105 and 107. (Yes, it has been a hot summer!)

The motorcycle was made in Canada. Most likely the computer that manages the motorcycle uses metric units of measurement. So, if the computer and sensors are dealing in °C but we ask it to display in °F there has to be some rounding error, especially since the display only shows integers.

So we made a simple table and messed around with the list of numbers that we saw actually displayed. Rounding the numbers got us close but certain values were still wrong. After some thought we figured out that the computer was using the floor function instead of the round function.

In the table below, we assume the computer is working from °C, so column A is a sequential list of numbers in °C . Column B is Column A converted to °F with one decimal point. Column C is column B rounded and Column D is Column B rounded down. Column D matches what we see on the display.

We have no idea why they chose "floor" instead of "round".

Personally, we think it is a bit inelegant to skip numbers, but we figure normal people will never notice it.

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Old 2015-09-06, 03:10   #2
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Uncwilly's Avatar
Aug 2003
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Originally Posted by Xyzzy View Post
After some thought we figured out that the computer was using the floor function instead of the round function.
I would submit that instead: They are using the INT() function or otherwise just lopping off the decimals. While this might not be noticeable in your area right now... In Winnipeg during the winter you might notice it. :rajula:
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Old 2015-09-06, 05:53   #3
Batalov's Avatar
Mar 2008

2·41·113 Posts

The Nissan Altima and Toyota Camry temperature displays have always done exactly the same (floor or int).
Because we don't care about mpg or any other types of display we always have our settings on ambient T, so we noticed for years the same effect as Mike.

Actually, for MPG display, values are skipped much the same way (because internally they are probably in L/100km.)
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Old 2015-09-06, 06:47   #4
S485122's Avatar
Sep 2006
Brussels, Belgium

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To avoid those problems just switch to the international units... What backward place still uses miles, gallons and other obsolete units ? The US of A are members of the International Bureau of Weights and Measures (BIPM).

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