The man who steals all the phones in Las Vegas - pinpointed precisely

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Some years ago, I drove an ageing and rather temperamental British sports car (as though there were any other sort).

It was handmade out of fibreglass - rather carelessly, if the truth be told - and excitingly unreliable. But it went like crazy and looked quite the Badger's. Parisians in particular used to drool over it. But no matter.

This car had an old-school speedometer - the sort that has a rotating cable running from the gearbox into the cockpit, and works by means of a spinning magnet and eddy currents.

It worked smoothly and accurately up to 50mph, but from 60mph to 80mph it just lurched happily, if rather drunkenly, between those readings.

Over 80mph (for example, on certain German freeways), it would steady out and work normally again, though you didn't want to try that too much lest some car part work loose and fly off, such as the gearbox.

But for all the wavering of its needle, I was never caught out or confused by this irreverent speedo.

Mostly, the law required me to be at 50mph or below, where the instrument was precise. Above that, if I needed precision I could just glance at the position of the rev counter or the rate at which the fuel gauge was going down. (The motor had a bit of a thirst, bless its heart.)

In other words, the speedo was self-documentingly imprecise. It reported with unambiguous visual clarity that I was between 60 and 80. In that sense, its accuracy couldn't be faulted.

Imagine, however, that it had been a digital speedo of similarly British automotive cantankerousness.

On a motorway journey, it would have swept smoothly up to, say, 56mph, and then jumped to 69.865443mph and stayed there until the next fuel stop, 145 miles later.

I wouldn't actually know at any moment if I were under 70mph, the UK motorway limit, and I wouldn't know that I didn't know.

This sort of false precision is a real problem in today's instant-facts-and-figures society.

If I ask Google, for example, for the "latitude and longitude of Sydney", it tells me that it can be found at 33.8683°S 151.2086°E.

To me, those co-ordinates imply a tiny area, expressed to with 10 metres: the sort of detail I'd need to describe exactly the lobby of a small, boutique hotel in the crowded part of the CBD. Which is exactly what it is.

That would have been fair enough as an answer if I had obviously been looking for the Vault Hotel at 122 Pitt Street, Sydney 2000.

But it's a misleadingly precise answer for a question that isn't about an individual hotel, but instead about a metro area of well over 10,000km2 that's home to nearly 5,000,000 people.

They simply couldn't all fit into the Vault Hotel at the same time, and anyway they'd run out of beer almost immediately.

So spare a thought, if you will, for Wayne Dobson, of Las Vegas, who's a repeat victim of what you might call "precise imprecision."

It seems that at least one mobile phone company has a truly dramatic flaw in its geolocation database. Whenever it knows that a phone is in his part of the world, but can't be more accurate than that, it says so in an unnerving way: it pinpoints his house.

It doesn't draw a little circle on the map to say, "That phone's probably in a 2km radius of here," or a jagged polygon to say "It's somewhere inside this grid of lines joining the following five transmission towers spread over an 8km2 area."

It as good as says, "Head to Casa Dobson. You'll find the phone in the kitchen, next to the kettle, under this morning's newspaper."

The problem is that this precisely imprecise data isn't just a theoretical hassle for telecommunications engineers in the field. It also gets shared with the sort of tracking software that you or I can put on our own phones in case they're lost or stolen.

So, aggrieved members of the public keep turning up at Dobson's house, shouting that they "have proof" that he's stolen their phone and ranting at him to give it back. No-one's popped a cap in his trousers yet, but you have to think that it could happen.

dobson-sign-500

Worse still, the police have turned up at his house, answering other people's emergency calls. In this sort of case, the cops are between a rock and a hard place. They have to attend, and they have to start by trusting the official data they're given by the dispatcher. They can't simply say, "Ah, that's Wayne's place - it won't be him."

And that brings us to the critical question: what to do about this sort of thing?

I don't have a glib answer, I'm afraid.

But I do urge you to be responsible and respectful about how you present your own data. False precision leads to false authority, and that is the sworn enemy of computer security, because it can lead you off on wild goose chases implementing policy that is not actually evidence based - it just seems to be.

In short, don't be afraid to use the words "about" or "approximately" in your answers, and do your best to quantify your imprecision, as engineers do when they write something like "250mm, plus-or-minus 5mm."

Yours sincerely,

Paul Ducklin
North Sydney

My current GPS location:

myloc-486

PS. The above location, seemingly precise to within 1% of a nanometre, and reported apparently without irony by my Android GPS app, is actually off by about 100m.

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50 Responses to The man who steals all the phones in Las Vegas - pinpointed precisely

  1. Jon · 586 days ago

    Once again a very informative piece presented in an easy to read/digest style +/- a smidgeon :)

  2. Garry Jantzen · 586 days ago

    What you are saying, briefly then, is that there is a big difference between accuracy and precision. Just because an instrument is precise doesn't mean it is accurate. This is also a big problem in testing. Just because a test has been administered and you can get results to 4 places doesn't necessarily mean that *anything* has actually been tested!

    • Paul Ducklin · 586 days ago

      I was going to say just that very thing, but when I looked up "accuracy" and "precision" in my trusty Oxford Dictionary of English, each referred in part to the other :-)

      So I decided not to tempt lexicographical censure.

      (Remember the classic example of the two clocks? One's broken and has stopped. The other is 30 seconds fast. So the former is absolutely spot on twice a day, whilst the latter is inaccurate all the time :-)

      • David Heath · 583 days ago

        But Paul, you've just created *another* problem.

        Although you are conscious of the fact that the stopped clock is correct on two occasions every day, you have no idea just when those occasions are!

  3. John Smith · 586 days ago

    I have that same Android app, and it does show the accuracy. However it is cut off in that screenshot.

    • Paul Ducklin · 586 days ago

      True. It said 96.0 metres. It was the ludicrous decimal precision I found amusing.

      But you're right...the app does give you some expectation of how good the readings are. What I can't say is how precise the accuracy reading was :-) I think it was out by more than 96 metres, but only a bit. The office is actually across the road, which is a dual carriageway. My GPS put me in in the nearby shopping centre, next to the station.

  4. Ben · 586 days ago

    Just a quick one, you're getting words a little confused about "precision", and "accuracy".

    Precision is all about how many significant figures your numbers are written to. For example, the speed on the digital speedo (69.864443 mph) is very precise, as it has a lot of numbers after the decimal place. However, as you mention, it's probably not very accurate, because it's probably a long way from the true figure.

    • Paul Ducklin · 586 days ago

      The difference between precision and accuracy is not as clear cut as you might like, at least in English written for a general audience. Here are Oxford's Finest on the issue, from the New Oxford American Dictionary.

      accuracy: the quality or state of being correct or precise

      precision: the quality, condition, or fact of being exact and accurate

      (Dont you hate it when that happens :-)

      My 69.864443mph figure has many significant digits and thus gives the impression of precision, but it is misleading to refer to it as precise, since it is wildly incorrect. This is what I call "false precision" above.

      • Mrs. W · 585 days ago

        Actually, precision has to do with reproducibility. Under the same circumstances, does the measurement come out the same, or is it wildly all over the place?

        A measurement can be wildly inaccurate, but if it is always off by the same amount, then it is still considered to be precise. You can see why this would matter for scientific purposes. If I measure the heights of everyone in the Sophos office and average them, then later find out that my ruler is a foot off, I can easily correct for that. But if the measurements are scattered -- if I'm sometimes off by an inch one way and 5 inches the other -- then my system is highly imprecise.

        I think the confusion comes from the fact that a measurement that has fewer significant digits is inherently going to be less precise because there's more leeway for scatter.

  5. Never rely on literary dictionary for the meanings of scientific/engineering terms. Even when you're writing for a general audience, it doesn't hurt to use them correctly — you won't confuse the general public and you'll keep your credibility with the technically literate segment of your audience. The speedometer was not less precise between 60 and 80 (the markings on the dial weren't farther apart in that range), it was less accurate.

    • Paul Ducklin · 586 days ago

      I'm not sure the editors of the Oxford Dictonary of English (the British flavour has lost the "New" designator as it's already in its third edition) would like to hear it called a "literary dictionary."

      And I'm not sure how spreading out the markings on a speedo would make it more precise. More legible, perhaps, or more usable. But not, ipso facto, more precise. I doubt that anyone - poet or engineer - would ever have described my speedo as "not less precise between 60 and 80". (Let's face it. The speedo was broken, defective, dysfunctional, not "no less precise." Trust me. I had many happy hours on the autoroute watching it wave carelssly at me.).

      Precision is determined by quality and correctness at least as much as by how neatly labelled the dial might be, surely?

      And I think that by mixing engineering and demotic (if that is the right word - I suspect it is not) English in a single document, you *will* frequently confuse the general public, especially when you consider how blighted by jargon the average technical writer's vocabulary and prose are...

      • Ben · 584 days ago

        I'm afraid (at least for Chemistry and Physics GCSE and A-Level) precision is effectively how many numbers you've been given. For example:

        The outside temperature (UK) is 108.597635548 degrees celsius. This is a very precise piece of data, but it is _NOT_ accurate, as there's actually snow on the ground ;)
        The outside temperature is 0 degrees is more accurate, but far less precise.

        Precision is easy for digital devices, but harder on an analogue scale. The general rule is half the smallest division.

        • Paul Ducklin · 584 days ago

          Many programming languages are the same. What the string formatting functions call "numeric precision" is actually nothing more than "how many digits would you like to print out when we convert whatever internal representation we have of your number into decimal notation."

          The concept of "being precise" is converted into "presenting redundant and misleading detail" :-)

  6. John Keating · 586 days ago

    Hmm, this debate might come in handy for Microsoft in the AV-Test fiasco ; )

  7. Niall Martin · 586 days ago

    The old problem of the difference between technical language and colloquial language. Philosophers, mathematicians and scientists do know the difference and observe it. Ordinary speakers need it explained to them, and good dictionaries need to distinguish.

  8. andy · 586 days ago

    This being in the US, he can probably sue - not just the company that's giving out false information, but also those making false accusations. There's certainly no way that company can say they are acting reasonably in publishing his address, if he's made them aware of the problem. The police should also act against company for wasting their time.

  9. Nomphra · 586 days ago

    ..and in a complete change of subject, I have a rather irrelevant question: What was the car? I'm going to have a guess .. TVR *something*?

  10. Francine · 586 days ago

    I have that problem once in a while with GPS since the late 90's in field work. I once checked the location of a claim post, got the numbers with a good precision (back then about 25-30 meters) and when I counter-checked the location on a map, the post was in the middle of a lake (I was on the shore of that lake just beside the claim post). It is a common known problem with those who regularly use GPS at work, now everybody has GPS locator in their phone and they are often way worst than old field instruments (100 meters precision at times), but not many are aware of this problem.
    I called that being precisely beside the spot!

    • David Heath · 583 days ago

      about a decade ago, a pal told me of the time he was using a marvellous new GPS system on a yacht race from Sydney to Brisbane. At one stage, the unit insisted that he was about 50m below sea level.

      ...and his feet weren't even wet!

  11. TonyG · 586 days ago

    People confuse precision with accuracy.

    I used to find this with digital signal processing (I'll simplify this) - suppose I have 4 bit numbers 0 - 15. If I add 16 of these, I will have an 8 bit number. If I now divide it by 16 I will have a number with 4 bits to the left of the decimal point and 4 bits to the right of the decimal point.

    Now you can argue that by averaging readings, I have ended up with a more accurate answer. But since I can only measure to the nearest bit, my original 4 bit number is really only a 3 bit number +- 1 bit. You can do lots of statistics, but adding 16 4 bit numbers will not give you a number accurate to 8 bits.

  12. Bob · 586 days ago

    Never mind accuracy v. precision: did you make up the phrase "looked quite the Badger's"? Never heard it before, got nothing out of Google ... but kudos for whimsical yet convincing neophrasis.

    • Paul Ducklin · 585 days ago

      Ah, I wish I hadn't used it, now I have to explain...

      ...it's a synonym for "the bee's knees", though it is not the badger's knees that are being referred to, it's his nadgers. Like "the dog's bollocks," except that badgers are generally even more ferocious when they want to be.

      • Bob · 585 days ago

        Very good ... should have worked that one out.

        My son built a similar but perhaps even more temperamental vehicle a few years back (Tiger SuperCat). Great fun but there's not much point in expecting useful information from the dials. Best not to take your eye off the road, really.

  13. TonyG · 586 days ago

    In the UK, your speedometer has to be accurate to +-10%. If your speedometer is digital, then it should be +-10% +- 1 digit, so at 34mph in a 30 limit you should not be prosecuted. But people are. Not only that, if you check out the speed camera calibrations, these are only done to the nearest 1mph (or at least the Somerset ones were when I last checked). Thus, with another +-1mph, even 35mph ought not to result in prosecution.

    Ford speedometers of the type Paul describes were notoriously non-linear - up to 50mph, OK, but from 50-70mph they varied wildly. I know, because I used to write electronic speedometer and trip computer software in the early 1980s and used to calibrate both the electronic and mechanical ones by keeping a constant speed over a measured mile.

    The difficulty I had was not with what to display when at a steady speed, but what to display when accelerating or decelerating - averaging to avoid flicker means that the value is always behind what it should be. You can use differentials and try to predict what it is from the rate of change to get something a bit more accurate. But what if acceleration is non-linear e.g. just after the point when a turbo kicks in and there is a surge of power?

    • MartynS · 585 days ago

      As I understand it, in the UK a speedometer can over-read by up to 10% + 4kph but may not under-read. (Construction & Use Regulations 1986). That's why people can be prosecuted at 34mph.

    • Paul Ducklin · 585 days ago

      My recollection of the relevant UK regulations is that the +/- 10% rule is an urban myth.

      Speedos may read too high, in accordance with a table that is IIRC not linear (see the SVA regulations), but may never read low.

      • DavidM · 585 days ago

        I'm sure you're right about regulations, but the association of chief police officers (ACPO) recommends prosecution at a speed of 10% + 2 mph, which most (?all) forces abide by - so the rule isn't an urban myth.
        http://www.cps.gov.uk/legal/p_to_r/road_traffic_o...

        • Paul Ducklin · 584 days ago

          Sentencing guidelines are just that - guidelines. They are no doubt influenced by the law about speedo accuracy, but they are not "the rule" about speedo accuracy.

          IIRC, UK road law requires that your speedo must "show your speed in MPH at a glance" (which is why km/hr speedos must be converted), and must never read low, though they may lawfully read high by an amount that is approximately 10% of your actual speed.

          From this has come an urban myth that a speedo may lawfully be inaccurate by up to 10% either way.

          It's simply not true - but is a good example of how a precise regulation can end up adapted by extrapolation into an inaccurate statement.

          Anyway, it doesn't matter what *your* speedo said, it's what the external measuring equipment said that matters.

  14. TonyG · 586 days ago

    What seems to have been forgotten these days is the difference between precision and accuracy. I grew up in the days of log table and slide rules - whatever the precision, the slide rule was only accurate to 3 significant figures and lof tables 4 significant figures. When calculators first came out, people suddenly thought they had phenomenal accuracy until you asked them to enter 45 sin cos tan arctan arccos arcsin and got an answer something like 67 (instead of 45). With sliderules and logs, these only gave you three or four significant figures; you then had to do another calculation to determine what the exponent was i.e. where to put the decimal point - this might mean that the answer was 365000 - this didn't mean that the answer was accurate to 6 figures.

  15. Leo · 586 days ago

    Clarifying the precision / accuracy distinction is not for this forum or my virtual keyboard. The point is the implication of the expression in significant figures. In the US 0 g trans fat means less than half a gram.

  16. dc55 · 586 days ago

    Thanks for the article it was hilarious and technical at the same time! The comments were great too (though I didn't read them all).

  17. Verr D · 586 days ago

    Maybe Dobson should start stealing phones! The lawmen would continue to treat it as a false positive. ;-)

  18. Freida Gray · 586 days ago

    In the USA there is a term called "death by GPS".This term refers to the fact that some (not sure of the exact number of ) people have died because they trusted the GPS mapping feature in their vehicles.Because there are fewer people living around areas such as the National Forest & the desert regions,there are fewer cell phone towers.This means that there are fewer information sources available to GPS locator/mapping devices.With less information available & sometimes out-dated information the information these devices give is not reliable.Trusting unreliable information in these areas can be fatal.

    • Mark Gardiner · 585 days ago

      While it's true that there are fewer cellphone towers in remote locations, this has absolutely nothing to do with the accuracy of GPS data, which comes from satellites

  19. Tom · 586 days ago

    No offense, mate, but I'd have preferred the simple facts about Wayne Dobson's problem with lost phones being tracked to him. The story of your British sports car belongs in a forum about British sports cars. Rule of thumb in reporting: who, what, where, when, why.

    • Paul Ducklin · 585 days ago

      Problem with rules of thumb is that they often lack both accuacy and precision...

  20. freedie · 586 days ago

    Wayne Dobson wins! He had to come up with something to divert attention away from his mobile nicking obsession.

  21. Jonathan Stec · 586 days ago

    Just a thought regarding the solution to this gentleman's problem of unnerved citizens marching to his front door: Have the police dept sign a petition to have the cell tower relocated to a "precise" spot that clearly is an empty field (with similar signage to the effect that there phone should simply be reported to the local police as stolen. That should tamp things down a bit.

    ~Jonathan Stec
    Attleboro, Massachusetts

    • Paul Ducklin · 585 days ago

      From what I've read and speculated, the problem isn't actually that the transmitter near his house (or this would surely happen to everyone near one).

      It's just that the geolocation data in this case is presented as spot-on though it isn't, and since it isn't in the middle of a lake or a field, the assumption is that the reading is precise and accurate.

      You see a similar problem on lots of IP geolocation maps. There's often a hotspot of dots somewhere in Kansas (Topeka, is it?), at the geogrpahical centre of the continental USA.

      In other words, the geolocation database has decided that it knows no more than "this is a US IP number", and has "approximated" by picking the centroid of the country to represent that fact.

  22. Sam · 585 days ago

    Never mind the precision / accuracy - if only they could spell metre!
    Meter: device for measuring;
    Metre: metric unit of measure.
    But then I'm a Brit!

  23. I always get cross with articles that show measures in one unit then convert to another with spurious accuracy, such as "The shark was said to be between 25 and 30 feet long (7.62 to 9.14m)". If the original is an estimate, how can the conversion be stated with such accuracy? Duh.

    • Paul Ducklin · 583 days ago

      Like, "one imperial pint / 568 millilitres."

      Sometimes, wiser minds prevail. In New South Wales, for example, standard beer sizes you'll find in pubs are derived from imperial measures, namely 10 fl.oz., 15 fl.oz and 20 fl.oz. (Note to US readers: the UK increased its pint from 16oz. to 20oz. in the mid 19th century.)

      They've been rounded to 285ml, 425ml and 570ml.

  24. John · 585 days ago

    Long winded story !

  25. Nigel · 585 days ago

    "But it went like crazy and looked quite the Badger's."

    Huh???

    I'm guessing from the context that "...looked quite the Badger's" means it looked great, cool, sharp, neato, bitchin', terrific, glorious, wonderful...and any other synonyms for "very good". But "the Badger's" is a new one on me. It's a possessive, so the Badger's WHAT? Part of its anatomy? Can you even say which part in polite company? Or does the initial cap in "Badger's" make it a proper noun that refers to something other than a badger?

    Actually, I'm not picking nits. I'm just fascinated by idiosyncratic terminology, and this being an international forum, I've learned to expect (and not make an issue of) spellings (meter vs. meter, defense vs. defence, ...etc.) or even semantic structure (different from vs. different to, ...etc.). I'm just curious about the origins of certain sayings, and "it looked quite the Badger's" is one I've never encountered before.

    • Paul Ducklin · 584 days ago

      See my reply to @Bob above. The parts referred to are the "nadgers", so "badger's nadgers" are like, well, like "bees knees", but not quite.

      The fact that I made it a proper noun was a literary device called "boosting the apparent importance a bit dramatic effect."

  26. Robert · 583 days ago

    I love these old cars that have the speedo generated by an 'actual cable' that goes into the engine.Rmind me of the old days of my youth, where one of us would 'borrow' a friend's Dads car. After the event we would pull out the cable end from the bottom of the car, attach a power drill going anti anti clockwise.. and roll the odometer back to before the incident.

    These days, the Dad would probably just flick you the keys without a second thought.

  27. Mary Floyd · 580 days ago

    The Queen of England says she's taking back her language since we [Americans] can't seem to learn to spell it properly. The Strines do better.

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About the author

Paul Ducklin is a passionate security proselytiser. (That's like an evangelist, but more so!) He lives and breathes computer security, and would be happy for you to do so, too. Paul won the inaugural AusCERT Director's Award for Individual Excellence in Computer Security in 2009. Follow him on Twitter: @duckblog