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My odometer can't count

  • 03-06-2014 8:46pm
    #1
    CiniO
    Registered Users, Registered Users 2 Posts: 16,069 ✭✭✭✭


    My car has a digital speedometer, and option to switch between MPH and km/h. When you switch speedometer from km/h to MPH, odometer reading is also switched from km to miles, as well as fuel consumption from l/100km to mpg.

    Anyway according to wikipedia, 1 mile is 1.609344 km.
    So when my odometer shows 100,000 miles, when switched to km, it should show 160,934 km.
    Unfortunately this is not the case.
    Recently car reached exactly 100,000 miles, and when I switched to km, it was exactly 161,000 km.
    That's 66 km extra.

    I wonder why did they do it? Surely it makes no difference for software counting those values if they put 1.609344 as mile or 1.61.

    Car is Honda Civic.

    Why is it like that?


Comments

  • #2
    colm_mcm
    Registered Users, Registered Users 2 Posts: 73,520 ✭✭✭✭colm_mcm


    When I divide one by the other on mine I get 1.61000693

    That'd be the same as yours so?


  • #3
    Mycroft H
    Registered Users, Registered Users 2 Posts: 9,313 ✭✭✭Mycroft H


    Probably just that; software limitation where it was rounded up to 1.61. Or a lazy programmer.....


  • #4
    Bpmull
    Closed Accounts Posts: 5,042 ✭✭✭Bpmull


    I wonder is it to do with the fact computer work in base 2 and then convert it to base 10 so we can read. Ie 5 to us is 101 to a computer. There is always round off error with certain numbers as a fraction in base 10 may be an infinitely repeating set of numbers in base 2. Either way I wouldnt be loosing any sleep over it.


  • #5
    PaddyFagan
    Registered Users, Registered Users 2 Posts: 1,146 ✭✭✭PaddyFagan


    I suspect that's it's down to the accuracy of the odometer - based on this http://en.wikipedia.org/wiki/Federal_Odometer_Act it's +\- 2.5%. Given that using a conversion factor with more that two digits of precision is pointless.

    Effectively all the readings are subject to that 2.5% up or down error bounds.

    Paddy


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