The Way These Oil Pressure Gauges Are Labeled Seems Bonkers

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I’m interested in the way our cars communicate with us. I think that’s why I’m so interested in indicators and taillights, and on the inside of cars, gauges. Gauges are especially interesting because while taillights and turn signals are how we use the car to communicate to other drivers, gauges tell us information directly from the car. No puppeteering involved, those little moving needles or digital digits are your car’s bits talking right to you. The way we choose to frame the information on gauges is interesting, too – I’ve explored it for fuel gauges a couple times, but today I was introduced to a really strange labeling convention for oil pressure gauges, and I needed to show all of you, stat. So, put your dropcloth down just in case this shocks any fluids out of you.

I was alerted to this by a reader named Nick who saw this interesting Reddit post, which showed an oil pressure gauge (in what I think is an old Alfa Romeo or maybe Fiat) that looked like this:


Do you see what’s going on there? Oil pressure is measured in terms of a unit of force per a given surface area. That’s because the oil in your engine is under pressure, which helps to force it through all those channels and the pressure helps the oil get between all of those spinning metal parts, forming a sort of fluid bearing so the metal bits can’t rub up against one another, in much the same way you or I are encouraged not to rub up against one another in, say, the checkout line at Target.

For most of our readers, the most common units used to measure oil pressure are pounds per square inch, commonly abbreviated as PSI. There are other ways to measure it, too, if square inches are just too Imperial for your Metric mind, like in Pascals (one newton of force per square meter) or as bar (which is 100 kilopascals).


But, let’s get back to our weird gauge here. It’s a gauge that measures in PSI, but instead of being labeled PSI like almost every other oil pressure gauge I can think of is, it’s instead labeled with this ridiculous rebus:


What, and I mean this earnestly, the fuck.

It may take you a moment, but I’m sure you see what they’re going for here: lb is the abbreviation for pound, the slash connotes the idea of “per,” then there’s a literal square, and then the ” which is the abbreviation for inch.

Is this just some weird Italian nonsense, since that gauge is a Veglia Borletti? I checked and, no, we can’t blame this on Italy, because it shows up in other company’s gauges, including Smiths and Jaeger, for example:


So, this seems to be A Thing, and looks like it’s shown up on a variety of cars over the years, from Alfas to Jags to Fiats to whatevers. I don’t understand why this would ever be considered preferable to PSI.

For one thing, it’s just harder to read. That reads like letter O or a zero, since plenty of typefaces square off letters like that. Then, the use of ” for inch is well enough known, but it’s a tiny symbol, and it can also mean seconds as in how you can break down degrees into minutes and seconds. I don’t know why you’d think this was talking about degrees on such a gauge, but I can easily see looking at it and reading “pounds per zero inches?”

Also, conceptually, it’s just feels wrong. It shows a literal square before the inches, like an object unto itself, when, really the “square” being implied is more of a mathematical square, a unit of area, one inch per side. And, yes, while that is a literal square shape, it just, I don’t know, doesn’t read like it should.

I think even using an exponent to denote square would be better, like

lb/” ² or lb/in ²

But even that isn’t great, if we’re honest. None of these are better than the simple PSI, which even takes up less room than lb/▢” anyway.

Does anyone prefer this? I suppose it has some aesthetic appeal, and if I had a car with this on a gauge you know I’d be all over it, showing it off to any poor bastard unfortunate enough to get within ten feet of me and my car.

You know what? Let’s a do a poll! I’m curious if there’s anyone out there who things the goofy letters-and-square-and-slashes-and-hashmarks bullshit is better than PSI, and if you do, I’d love to know why, so tell me in the comments after you vote!




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67 Responses

  1. One of the race-y things I love about Porsches (esp older ones) are the gauges…sure, the giant tach right in the middle + offset speedo is the best element, but I also enjoy the separate gauges for every aspect of one’s oil – level, pressure, and temp.

    Whenever I get to drive one, I still get confused which one is which, at a quick glance. I swear I can feel the car’s Teutonic sternness harshly judging me.

  2. I chuckled when I caught the gag. Weird nomenclature is fun. I kinda want one for my dash binnacle. To go with the ‘essence’ gauge I want just cause it’s weird. And now, having looked, it seems I can buy one in black instead of old-fashioned white/brass surround which definitely wouldn’t fit the era of my ride.
    Now I gotta find a boost gauge in pounds per square so all three can be strange

  3. “Gauges tell us information directly from the car. No puppeteering involved, those little moving needles or digital digits are your car’s bits talking right to you.”

    This is why I hate gauges that are actually idiot lights. For instance, both the oil pressure and temperature gauges in my Miata have big ol’ dead spots in the middle. (Lots of cars are like this, actually. My Subaru’s temperature gauge won’t move between about 150°F and 250°F) As long as the coolant temperature is somewhere within a wide band of acceptability, the temp gauge needle will sit at 11 o’clock. As long as the oil pressure is even vaguely OK, the oil gauge needle will sit at 1 o’clock. If either needle deviates even a little bit from those positions, your engine is probably already fucked.

    They *look* like they are giving you real, nuanced information but it’s a sham. All they are actually telling you is a binary OK/Not OK. That should be handled by an idiot light, not a gauge. If you deliberately fuck a gauge so that it doesn’t behave the way the person looking at it expects it to, you are committing a crime against engineering, design, and sanity.

  4. According to Google 1 bar = 14.504 pounds-force per square inch
    (I thought it was 16 psi but whatever, perhaps I’ve been living at an unusually low altitude)
    Anyway, shouldn’t a pressure gauge that measures in bar start out at one not zero?
    Unless you are in a vacuum you have one atmosphere of pressure ie one bar.

    For that matter, shouldn’t a gauge that measures in psi start out at 14.5 or whatever?

    As for the ???? “ , I prefer the exponential notation but that picture of a square probably makes mor sense to more people.

    1. Any pressure gauge is just showing the difference between the pressurized container and ambient pressure. The difference starts at 0 and goes up from there. If you fill your tires on mount everest and the gauge started at 14.5 psi, you’d be almost 10 psi to high.

    2. Great question, “PSI” or any general use gauge, implies “zero” is 1 atmosphere, 14.5 PSI, 1 Bar, 760Torr what have you. In some industries and scientific applications, this isn’t the case, so any gauges in these areas are labeled “PSIG” meaning PSI gauge. If a gauge is labeled “PSIA” (absolute or atmosphere), it will read 14.5 disconnected from anything. A common use of a PSIA gauge is a boost gauge in a car, because even though it sits at “zero” when the car is off, it reads “vacuum”*, so it’s a PSIA gauge, with it’s scale off by 1 Bar. So while sure, when you put 30 PSI into your tires technically they have 44.5 PSIA, but why confuse people?
      *vacuum isn’t an accurate term either as it implies nothing, the technically correct term is RP or reduced pressure, anything below 14.5PSI is RP, we use the Torr range, because as I stated 1 ATM = 760 Torr, that gives you a lot of resolution without going into decimal places.

  5. Unusual, perhaps, but mind-boggling? I don’t think so — just read it, in order. Done.

    A little more perplexing was the first time I was reading an old 1050s British drawing for a gear, and in the material specs, for yield strength and UTS where I would expect either Mpsi (Imperial) or MPa (metric), it was marked T/□. Which turned out to mean tons per square inch.

    1. Came late to say this. Old school Architects and Engineers used it, but it died out in the 60s and 70s. when I started my career in 00, some of those old timers were still around.

  6. lb in^-2 would be a mathematically correct formulation. BUT the Smiths gauge in my Morgan is calibrated in the square thingy which I can’t type AND kg sqcm. That is not only not a metric unit if it was written properly (kg/sq cm) but it isn’t, mathematically, a unit of pressure. Shortly after my Morgan was made, German company VDO bought Smiths. I imagine kg sqcm caused them physical pain.

  7. That’s kind of an old-school engineer’s/architect’s style of notation. Back when we put pencil on vellum or pen on mylar, the literal square box to indicate square units was pretty common. I don’t know that I would argue that it’s a preferable approach, but I’ve seen that shorthand so many times as an architect that I didn’t bump on it.

    1. I chuckled too, but there’s also a genuinely practical aspect to this (surprising in a bit of Italian car engineering) – *internationalisation*. “PSI” stands for Pounds per Square Inch – IN ENGLISH. To anyone else, it would feel as uncomfortable as having “圧力” staring at you (that’s “pressure” in Kanji BTW)

      EVERYONE can (with a bit of head-scratching) work out that this is showing:
      OIL (the universal dripping can icon)
      PRESSURE ( because lb/▢” is most definitely not a LEVEL nor a TEMPERATURE )

      No need to have specific gauge faces for different languages/regions. If you’re clever you apply this to your whole dash module and thus you’ve got, at the very least, the whole of continental Europe (left-hand drive, km/h, km, and temperatures in Celsius) covered with one part number. Winning!

      1. But then shouldn’t there also be an internationalized pictographic version of “lb” or “lbs”? I mean, I doubt that most people speak Latin. My point is, even if we don’t speak Latin, we’ve all basically accepted the fact that “lb” and “lbs” stands for “pounds”. Even though “PSI” is an English acronym for “pounds per square inch”, is it as equally recognizable internationally as “lb” is for pounds? If so, then I’d argue that “PSI” would be the better choice purely for clarity. “PSI” uses all letters, whereas the ” lb/□” ” uses a combination of letters and pictograms. This requires extra processing for the brain to convert the pictogram “□” to the word “square” and the ” to the word “inch”.

      2. Re: “universal dripping can icon”

        My brother told a story of his daughter’s long-term use of some guy’s BMW, and eventually complaining that the “little teapot light” was *always* on . . .

  8. Interesting timing. While doing my thing as a Tech Writer this morning, I cam across this convention in a document I was editing. Initially I asked the author, and then my engineering brain kicked in to reveal that it was a square.
    It was in a line of specifications for material that included a need for such a measurement.
    I left it in place.

  9. I totally agree re: “ridiculous” and “wtf” and all that.
    But for the poll I voted A, ‘ cause there’s just not enough *delightful* absurdity in my life — and that PSI alternative notation is grapho-phonetically, hieroglyphically, parallel-universally delightful!

  10. I’d really like to know what John Davis of Motorweek thinks of this weird PSI symbol, given his affinity for gauges. Come on, Jason. Get him on the blower and do some REAL investigative journalism.

    What would make this better is if the metric version was just a “|” or “_”

    You know….for bar.

    …………jokes are funnier when you have to explain them………..

  11. Started to think about using international symbols on all gauges and realized most would be very difficult. You almost have to commit to some country’s unit of measure and maybe put 2 units on the scale. Quantities are easy with 0 to 1 and fractions or empty circles/half full circles/full circles, but that doesn’t work with other gauges.
    We could be getting into developing new international symbols here.

  12. Oh, speaking of initially confusing gauges, does anyone get confused, at least briefly, when driving a car with identically sized speedometers & tachometers where the tach is calibrated x100 rather than x1000 so both gauges have identical numbers? So 30 on the x100 tach is 3000 rpm whereas the x1000 tach will simply have a 3 which seems clearer & less likely to be confused with the speedometer with its double digits (well, until one hits 100 mph.) Why would anyone want x100? Is there a legit need for such a convention? The x100 tach seems particularly prevalent amongst modern cars & seems especially typical of German cars, at least in my relatively limited experience, though I do have a lovely VDO tach from a Porsche 356 that is calibrated for x1000 UPM (in green with a red trapezoid behind the “6.”) And I’ve seen tachs calibrated x1 on brass era cars which does make for a rather crowded field to read with all those digits, especially the zeros, so it makes sense to increase the multiplication for a cleaner design & for clarity (though the x1 tachs can indeed be easier to comprehend more readily, perhaps ironically.) That said, it doesn’t make sense for the x100 to be seemingly the most common multiple. Yeah, a deep dive on tachometers & calibrations thereof would be informative & greatly appreciated…

    1. Back in High School, my parents had an ’86 Escort wagon 5-speed that I drove all the time. I eventually wanted to get my own car and test drove a Dodge Daytona that I had fancied. So my buddy and the sales rep piled into the car and took it for spin. On a small, two-lane road near the dealership, I struggled to get the car to get up to the 45mph speed limit. After getting back to the dealership, I realized that a) the tach was x100, and b) the tach and speedometer were flipped compared to the gauges in the Escort and I had been checking the tach. To this day, I have no idea how fast I actually had that car going, but my friend said that the sales rep in the passenger seat seemed awfully uncomfortable during the test drive…

  13. Hey, it’s always nice to have a little levity in automotive gauges! And, usually, if one is initially confused by the square looking like a zero or the letter “O” a moment’s inspection will show the “B” in “lb” (and also the “S” in “lbs”) to be rounded so it’d follow that a zero or the letter “O” would be similarly rounded whereupon it becomes obvious that the symbol is indeed a square. Yes, I daresay we all could stand to have the random rebus in our everyday lives.

  14. As an engineer, I like the unambiguousness of PSI. I know what it stands for, so does most everyone involved with cars.

    As a human, and someone with a creative/artistic bent, I love the weird little symbol.

    If I’m designing a system for the masses, I’d go with PSI. If I’m designing something for me, or a close friend, I’d go with the symbols.

  15. Gauge trivia: Certain Renaults from the early 1980s had oil LEVEL gauges. Obviously this only worked when the engine was not running; the needle vanished on startup. IIRC, it was inset into either the speedo or tach.

    A Toyota Echo I once drove — don’t judge — had a blue light on the dash. It went out as soon as the engine’s coolant temp started to warm up. No temperature gauge and, of course, no oil pressure gauge.

    Can’t wait ’til Jason dives into the wild & wacky world of fuel gauge markings! From “E to F” to “0, 1/2, 1/1,” there must be stories to be told….

    1. Older Porsches have the oil level gauge, with the same proviso.

      And yeah, I freaked out the first time I was driving one and it dropped way down. After a heart in my throat pull-off, I felt better fast that I hadn’t just in fact nearly destroyed someone else’s vehicle. Another good reason to always keep the owner’s manual in the car.

      Fuel gauges were I think 2 weeks ago; it’s worth a look up for sure. My favorite were the ones with actual liter (b/c we’d never get that kind of precision here in the States) fuel volume markings.

      1. Guess I’m always a day — or a week — late and a gallon short….

        Had the same reaction to the oil level gauge. Reminded me (and not in a good way) of my Renault 5’s dash with its bank of warning lights for oil press, charging system, brakes, etc. When one lit up, they ALL went on. Didn’t make diagnosis easy.

    2. Some old Citroens had them too; my BX has a combined oil level/pressure gauge; when the engine’s not running, or for a couple of seconds after startup, it shows the oil level, then switches over to pressure when the engine’s running. Not entirely sure how accurate it is; seems to read in line with the dipstick though.

    3. Was there, got the t-shirt. 1989 Renault Espace. When switching to “Ignition”, the oil gauge indicated oil level. When starting the engine it would indicate oil pressure. Said needle would suddenly drop when revving on cold days (“thick oil”) to prevent excessive pressure in the lines/connections. There also was a turbo boost gauge which I prioritized reading when driving.

  16. I would actually question the need for actual units on the gauge… I’m pretty sure the vast majority of drivers have no real idea what is the optimal psi range for their particular engine. I’d prefer to see the gauge done in a nice, clear red-green-red format, clearly labelled “Pull over, yer oil-pump’s f*cked!” with the green bit as “Yer good to go” and the final red zone as “I canny hold her Cap’n, she’s gonna blow!”

    1. I think it started with later Fox Bodies, but Mustangs used to have the word “N O R M A L” as the it’s all good range on the gauge face.

      Mine (an SN95) just has a more abstract dotted curve bracketed by red.

    2. Most cars, if they bother to have gauges for temperature or oil pressure at all, are like this—no units, just a couple of vague, unlabeled tick marks and maybe a red zone on one end. And on most cars, those unlabeled gauges are actually just idiot lights in disguise. The needle will sit at some predetermined spot as long as the oil pressure or temperature is inside some wide window of OKness, and if it moves even a little you have a big problem.

      I hate it. It doesn’t just give less information, it also gives the wrong impression of what information it’s giving. It’s fine if most people don’t care about temperature and pressure gauges (let alone voltage), but if you’re going to put them there then they should be reasonably accurate and have units on them. Dummy gauges are stupid.

      On modern cars especially, there really should be a “power user” or mechanic-type interface where you can get access to all this kind of information on a screen. There’s no reason why a modern car can’t show coolant temperature, oil pressure, and whatever other sensed or calculated statistics the ECU is working with. It doesn’t have to do it all the time, and it doesn’t have to do it if the driver doesn’t want it to. But there should be an option, because if you know what you’re looking at that kind of info can be hugely informative—and it’s *there*, it’s just that the designers decided you can’t have it unless you buy special diagnostic tools.

      I wish cars weren’t getting progressively more dumbed-down. I’m (mostly) not against all the fancy new tech that makes cars faster, more reliable, safer, and more efficient. It’s great, and I do get that it adds complexity. But not all drivers are ignorant, lots of us could handle the complexity and benefit from more insight into what our cars are doing. I’m not asking for it to be on permanent display, just give us an option!

  17. I never noticed it, until I read this article and walked out to my Midget and sure enough. But I like it. All the cars you listed that came with these kind of gauges are kind of weird. So it fits right in. Fiats, MGs, Jags, Alfas those cars are all a bit unique. This is fitting. Those wacky Europeans!

  18. You know, I miss when gauges actually used real units of measurement.
    lbs/in^2? MPH!? BAH. Give me back my furlongs per fortnight, inches of mercury (very easy to make those gauges,) and piston-face ft/s!

    1. If that has to be quantified, it should be in cubic inches, not square.

      (Also, this shouldn’t need to be stated, but none of us here benefit from knowing the volume of removed hemorrhoids. Unless you can make them relate to something automotive, somehow! )

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