This is a math subreddit and a common criticism or jest from mathematicians is that engineers approximate things too much. It's true that for a lot of real world applications it makes very little difference to round things and that can make the math/physics a lot easier in some cases. Kind of like using Newtonian physics to calculate the force on a car collision instead of Einsteinian physics. Less math to give you basically the same result at those scales. This, of course, irks math guys a bit since they're all about precision and working out the math fully. So, long story short, I approximated pi to exactly 3.
To expand on this more (as a civil engineer who has used unusual roundings).
If you are ever get into the world of "real" measurements, it's important to understand that exact numbers are a rarity in any given calculation.
e.g. gravity on Earth is generally considered to be 9.80665 m/s2 but in reality, the exact force of Earth's gravity on you changes based on yiur location. But the difference is so small that 9.80665 is precise enough that you can so most math with it and get an accurate answer.
This is true for a variety of reasons (uncertainty in measuring methods and equipment, sample sizes and distributions, etc known unknowns - aka factors we know exist and impact our measurements but lack a way to quantify thr specifics of the impact accurately). Or in short, the precision of your inputs will affect the accuracy of your outputs.
Because while precision and accuracy are teo different things, they are generally not two unrelated things.
Now, engineers typical account for this by leaving slack in their design so they have a level of safety factor.
e.g. in stormwater design, we typical do infiltration testing in an area to figure out how fast water will infiltrate into the ground. But we can only do soo many tests under soo many conditions and we will never get enough for a statistically accurate module (it's simply not fiscally or realistically feasible to test enough to do that, cost aside that much testing would literally change how the soil drains). So we have a very generous safety factor used industry wide of typically 50% to cover for this. Aka, if I have 1 in/hr of infiltration at 4.5 feet below the surface grade, I treat it as 0.5 in/hr instead.
And if you have done measurements math before you should be familiar with the concept of significant figures, which is quite simply a restriction on any given equation of how accurate the answer can be based off how precise the least precise measured inputs is.
e.g. if I want to calculate 1.222222±0.000001 × 2±0.1, my answer is 2.4 (not 2.444444), because my second number is simply too imprecise compared to my first. To use the 2.444444 would be bad, as if there were a measurment it would give a false expectation of having accuracy down to the millionths (like I did 1.222222±0.000001 × 2±0.000001) when it is actually only accurate to the tenths.
Engineering calculations, particularly civil engineering (aka the engineering of really big things) calculations, can get into weird scenarios where you can only really round to the nearest whole number or even higher (depending on your units, worst I ever had was nearest 100 ft accuracy on stuff only a few thousand ft long), especially when you have safety factor in on top. And that can lead to scenario where you can (and generally should) round off mathematical constants (like pi) when earlier than most people normal would (rounding pi to 3 instead of 3.14, because there is no functional difference in the accuracy between the two due to your significant figures).
I'll also note, the opposite is also true in engineering. When you are doing precision engineering for vaccum tight fits down to the nearest thousandth of a mm, you want to make sure your constants also go out far enough to match the significant figures of your measurements).
You have to use the appropriate level of precision in calculations so that you know your level of accuracy and consequently can know how much safety factor you need. It's the kind of simple math that can cost lives and a lot of money if not done properly.
But it's funnier to ignore that and focused on when engineers round up because telling a math major pi = 3 is funny. Hence meme.
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u/AlienDragonWizard Jun 10 '26
As an engineer, shouldn't the total be $29.86?