Transport software company increases chance of errors by using dual units

Jaama, a transport software company, advertises its MyVehicle App software product on its website with images showing that it uses both kilometres and miles. 1 Using dual units within software introduces the possibility of conversion errors and unit mix-ups. There are real-world examples of errors arising from the use of dual units in transport. Some are described in this article.

In 1999, NASA lost the Mars Climate Orbiter due to a mix-up of metric and imperial units. The loss of the mission to Mars cost $327 million. 2 3 This error arose from a discrepancy of the insertion altitude of the spacecraft when it entered Mars’ atmosphere. The main cause of this discrepancy was software supplied by Lockheed Martin produced results in United States customary units, contrary to its Software Interface Specification (SIS). NASA had another system that expected these units to be in SI units as required by the SIS. There was one software system that calculated the thrust in pound-force seconds and another one that used newton-seconds. The trajectory calculation software expected these results to be in newton-seconds to update the predicted position of the spacecraft. The results were incorrect by a factor of 4.45 newtons.

The Tokyo Disneyland’s Space Mountain roller-coaster derailed because of a specification error that arose from a mix-up between metric and imperial units. 4 5 6 Luckily, nobody was injured.

In 1983, Air Canada Flight 143 ran out of fuel about an hour after take-off. The pilot had to make an emergency landing at an airfield in Gimli. Faulty conversions arise from a mix-up between pounds and kilograms when calculating the density of the fuel. This led to the plane to be filled with less than half the amount of fuel required for the flight, so the plane ran out of fuel in the middle of the flight. Passengers arrived with light injuries, but it could have been worse.

In Jaama’s “Service, Maintenance and Repair” software screens, I see a Distance column with only numbers (but no units). 9 10 11 It is unclear to me whether these numbers represent kilometres or miles. This ambiguity would be removed if Jaama just used one system of measurements. Don’t Jaama staff realise that they don’t need two systems of measurement?

Why haven’t Jaama staff learnt lessons from errors like the ones described above and avoided the use of dual units? Using a single system of measurement would avoid these problems. By contrast, using dual units creates risks of conversion errors and unit mix-ups.

Sources

  1. https://www.jaama.com/myvehicle-app/
  2. https://everydayastronaut.com/mars-climate-orbiter/
  3. https://en.wikipedia.org/wiki/Mars_Climate_Orbiter
  4. https://www.nist.gov/pml/owm/metrication-errors-and-mishaps
  5. https://prezi.com/vxrvoz17nxz1/disneylands-space-mountain-unit-mishaps/
  6. https://en.wikipedia.org/wiki/List_of_incidents_at_Tokyo_Disney_Resort
  7. https://usma.org/unit-mixups
  8. https://spacemath.gsfc.nasa.gov/weekly/6Page53.pdf
  9. https://www.jaama.com/plant-and-asset-hire-management/
  10. https://www.jaama.com/vehicle-management-software/
  11. https://www.jaama.com/fleet-maintenance-software/

4 thoughts on “Transport software company increases chance of errors by using dual units”

  1. My criticism would be of the Minstry for Transport, rather than Jaama. This is a very comprehensive software plan for fleet users, who use, among other things, tachographs, which work in kilometres, whereas road signage and vehicle odometers use miles. Jaama is trying to be all things to all customers. It is Hobson’s choice really. Focus on the metric side of things and the imperial pals will complain – and vice versa. Metrication is already built into our transport system in many ways. Until the government finishes off the job there will continue to be these sources of error.

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  2. My 2022 Renault Arkana is switched to metric, with the exception of the odometer and trip meter, and consumption (mpg, tho I am unaware of anyone purveying motor spirit in any kind of gallons).

    The dashboard display helpfully shews the current speed limit—in miles per hour—with the equivalent in km/h. The conversion works just fine. Every time. Even when the GPS, in the middle of town, where the limit is clearly 30 mph, decides that it should be 100 mph, and converts it correctly to 161 km/h.

    This not the first of my cars to do this. The first time I experienced this phenomenon was on a variable speed limit section of M 25. The displayed speed on the gantry was 50. The car converted this erroneously to km, but displayed it as miles. Then it converted it from miles to km and informed me that the speed limit was 129 km/h.

    ”Houston…”

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  3. If speed limit values are converted to a supplementary unit, it’s important that any rounding that takes place should always be down, and never up.

    This is how metric supplementary values are calculated for speed limits in the Highway Code (Rule 124).
    e.g. 30 mph (48 km/h), 60 mph (96 km/h).

    https://www.gov.uk/guidance/the-highway-code/general-rules-techniques-and-advice-for-all-drivers-and-riders-103-to-158

    However, my car satnav (which is set to metric units) rounds values up, e.g. a speed limit of 30 mph is shown as 49 km/h, and a speed limit of 60 mph is shown as 97 km/h. By definition, any supplementary value that is rounded up exceeds the primary legal speed limit.

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  4. A speedometer will generate a reading in user units that need to be converted to mph or km/h, m/s or any other unit that might be appropriate (some migh prfer furlongs per fortnight 🙂 ). User units depend on the way in which the signal is captured. For example, “propshaft rotations per 5 seconds” might be a suitable user unit if the electronics behind the data capture consists of a proximity detector that triggers a pulse every time the propshaft rotates and every 5 seconds output the pulse count. In a digital dpeedomeer display, this count should be converted directly to every unit of measure that is displayed, making it impossible to tell whether the mph or the km/h reading is the greater.

    In practice, car manufacturers migth be tempted to use km/h in the basic system rather than mph because the km/h market is larger. A conversion to mph is then just an “add-on”.

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