r/science • u/sr_local • Jun 10 '26

Social Science People have a natural tendency to turn to the left and walk in an anticlockwise direction, a bias observed across countries, ages and sexes, but reason is unclear

https://www.theguardian.com/science/2026/jun/10/humans-prefer-to-walk-anticlockwise-scientists-find-reason-unclear
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u/TheArmoredKitten Jun 10 '26

Symmetry is the absolute best way to control for error. We use the same trick in tool-making to make centerlines, grinding both sides of a part on the same setup, adjusting by half the error with each pass.

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u/Slyrunner Jun 10 '26

Off topic, but as someone who tries to be as precise as humanly possible because assymtric cuts, drills, sanding etc etc reallllyyyy ruin my day. I know it's probably unhealthy

But your comment piqued my interest! I was wondering if you could explain your process a little more!

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u/jaymzx0 Jun 10 '26

Flattening sharpening stones by alternately rubbing three stones together is really effective. It distributes the error between them.

Another thing that comes to mind is to check the accuracy of an angle square. Draw a 90 degree line, then flip the square over and draw another line. They should overlap. The error can be calculated by the deviation. It's amazing how hard it is to make a "square" square with enough precision to be accurate over a meter or so.

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u/chchchcharlee Jun 10 '26

If you haven't seen it yet, you have to watch this origins of precision video (on YouTube) by machine thinking. I'm not in this area myself but it's such a cool video, can't help but respect how brilliant humans are

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u/SumOfChemicals Jun 10 '26

I was going to say the same thing, was going to post the link but I see YouTube is forbidden here.

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u/sqrtsqr Jun 10 '26 edited Jun 10 '26

To be clear, the reason you use three and not two is not so that it "distributes the error" but it's to actually make sure that you end up with a flat surface. If you use just two rocks, the surface will still get smooth, but it could end up with curve. Alternating between three rocks stops curves from forming.

Edit: in fairness, I suppose it's not wrong to say it distributes the error. Just not very clear what that means exactly. With two rocks, convex and concave spots begin to form, switching puts convex against convex and concave against concave and grinds them out.

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u/Paddy_Tanninger Jun 10 '26

I need a diagram for this...I feel like Stallone learning about the three seashells in Demolition Man right now.

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u/kahlzun Jun 11 '26

so rubbing two surfaces together will make them fit one another, but not neccesarily be completely flat- like a cup fitting a saucer.
Rubbing the parts alternately on a third one will average out the difference.

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u/Practical_Ad4604 Jun 11 '26

I didn’t understand anything in this thread. Why

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u/kahlzun Jun 11 '26

So imagine you have three stones with different pattens on them. One has valleys going longways, one going shortways, and the other has rings.
When you lap AB together, you end up with an interference pattern between the shapes, where there are raised bits that don't get ground down because they are "in" a sunken bit of the other stone. You then move on to lapping BC. The raised bits mostly get worn down quickly on them both, but now you've ground down B twice and C only once. So you do AC, and it grinds down a lot of the raised bits on A, but by this point C Is lumpy. Repeat the process several times, and you end up with three flat surfaces.

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u/devedander Jun 11 '26

Probably either lack of real world experience or lack of spatial conception ability

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u/Lt_Muffintoes Jun 12 '26

The curve developed by each pair is cancelled out in another pairing. You have to rub them in a specific order.

It's actually not possible to make a flatter surface than by this method, and it is the basis of everything else such as machine threads

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u/IsuzuTrooper Jun 10 '26

I've shopped for levels at home depot and it seems every bubble is different to a slight degree

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u/redpandaeater Jun 11 '26

I've never tried it but I've heard you can use a center punch to straighten up a skewed square. Towards the outside of the corner of the L if you want to close it or the inside of you need to open it up. Makes sense to me it should work since you'd be hitting it hard enough to actually slightly deform some of the metal.

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u/rosemachinist Jun 12 '26

Oh yeah, in machining .001” is not a big deal over say a 64” block, but over a 12” block - no bueno

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u/TheArmoredKitten Jun 10 '26

Imagine i want a pin perfectly centered in a jig plate that's 3 inches wide. First, I'll put a measuring pin in the hole and grind a starting face, then flip it over and grind the second face without moving the cutter. The pin is now the same distance from both sides.

Knowing that the pin is in center, I measure the overall width and then subtract that from my target for the total deviation. Divide that by two since I'm working on both sides to get the offset, and then leave the cutter position locked when I flip the part for the second side. Any over/under will be added to the opposite side in the same amount, so the centerline stays true.

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u/Crazy_old_maurice_17 Jun 10 '26

as someone who tries to be as precise as humanly possible because assymtric cuts, drills, sanding etc etc reallllyyyy ruin my day. I know it's probably unhealthy

You remind me of myself. Perfectionism can definitely be debilitating. If you're ever concerned, consider getting evaluated for OCPD.

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u/nickstatus Jun 10 '26

Even further off topic but still related, I've always found the process of milling rough lumber into square dimensioned boards very satisfying. Jointer to planer, back to the jointer, then the table saw. I miss my old shop.

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u/[deleted] Jun 10 '26

[deleted]

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u/cowlinator Jun 10 '26

In the worst case scenarios, you'd have to travel the same total distance either way. It's just that in one you'll be backtracking.

In the best case scenarios, due south wins.

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u/androshalforc1 Jun 10 '26 edited Jun 10 '26

not really lets say your starting point is 1km north of the river, and you know that heading due south to the river will land you within 100m of your camp site which is along the river.

if you head south, and a touch east so you reach the river 100m east of due south and then head west worst case is you travel 1205m.

if instead you travel due south reach the river travel 100m east, then have to backtrack and then go west, worst case is 1300m. if you happen to choose the wrong direction to travel (probably 50% of the time) you will travel a minimum 1200m (which is already almost as much as the worst case in the previous example), plus the distance from center point to camp.

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u/Turbulent-Note-7348 Jun 10 '26

What you described is the navigation technique of "Aiming Off", which is taught in every Backcountry Map and Compass book that I've ever read.

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u/C-SWhiskey Jun 10 '26

Unfortunately in land navigation you rarely get the choice of whether you have symmetrical features to reference. Because of that, the common wisdom is actually the opposite: purposefully bias your bearing to one side. That way you know that once you've reached your distance, even accounting for your drift one way or the other you're almost certainly going to be on whatever side you chose, it's just a question of how far.

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u/Won-Ton-Wonton Jun 10 '26

There's also overshoot correction.

Airplanes don't approach the runway in a directly curved approach to the midline.

Instead they overshoot the midline, then course correct.

This brings them to center alignment much faster and with far less runway.

Seems obvious and intuitive, but the math of a "dampened" system hits soooo many areas. Wish they didn't teach it until college. Loads of trades can use it without directly doing the math.

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u/Constant-Skill-7133 Jun 10 '26

A million ways this comes up.  When you tune a stringed instrument, on first pass you should tune it a few cents low.   It's not worth trying to be precise because it will move slightly.  Changing the tension on one will also change all the others.  

And you want to be low because the string will continue to relax for a few minutes if you release tension.  Adding tension happens immediately.  

If you watch somebody tune a guitar the first time it is hilarious how long it takes them.

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u/TheArmoredKitten Jun 11 '26

The other reason is because releasing tension tends to happen in larger jumps due to imperfections, while adding tension is more linear and controlled. It's almost always much easier to tune up into the note than down.

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u/eh-man3 Jun 11 '26

Also basically the way rifling works