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      07-08-2019, 11:49 AM   #1
russelldav
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Difference between HUD and iDrive distance

Spotted on my route today that the distance to go on the HUD was always 1km less than the iDrive. I would have thought they'd use the same data source - I guess not!?

HUD: 53km
iDrive: 54km
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      07-09-2019, 08:25 AM   #2
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Can someone else verify if this is a bug or a one off? You just have to set a destination to find out.
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      07-09-2019, 08:34 AM   #3
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Quote:
Originally Posted by russelldav View Post
Can someone else verify if this is a bug or a one off? You just have to set a destination to find out.
I've been meaning to check, but circumstances haven't presented themselves yet. It really should be the same, but if not, it could be a difference in rounding algorithms by two engineers implementing each system without a fully defined spec: one truncates and one rounds when displaying km-level range, and possibly combined with variance in display value storage precision, or something like that. As such, it might be very intermittent in practice.
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      07-09-2019, 08:42 AM   #4
russelldav
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Quote:
Originally Posted by LexxM3 View Post
Quote:
Originally Posted by russelldav View Post
Can someone else verify if this is a bug or a one off? You just have to set a destination to find out.
I've been meaning to check, but circumstances haven't presented themselves yet. It really should be the same, but if not, it could be a difference in rounding algorithms by two engineers implementing each system without a fully defined spec: one truncates and one rounds when displaying km-level range, and possibly combined with variance in display value storage precision, or something like that. As such, it might be very intermittent in practice.
I imagine you're right.

Reminds me of the exact same bug on a Hawk Mk. 120 Jet Trainer when I used to support the Avionics. The HUD and Barometric Altimeter were always off by 1mbar and it used to drive the Pilots wild. The reason then was two data sources - the HUD was driven by a smart air data probe and the Altimeter by a mechanical barometer.
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