The actual purpose is to weigh a human who has trouble standing on a scale. Idea is put one scale under each bed leg and add up the 4 readings to get the weight of the bed. Then do the same when the human lays down on the bed, and subtract. this work? Thanks. 2601:644:8581:75B0:0:0:0:55E8 (talk) 08:54, 8 March 2025 (UTC)[reply]

Why not reset the scale to zero after placing it under the bed legs? By doing this, you simply add the four readings together. Stanleykswong (talk) 09:01, 8 March 2025 (UTC)[reply]

A bed would be too heavy even for four normal bathroom scales. Better to use a plank of wood and two scales. Shantavira|^{feed me} 09:11, 8 March 2025 (UTC)[reply]

The weight of the IKEA NEIDEN bed frame is 14.89 kg and the weight of the LUROY slatted bed frame is 8.51 kg.  The bed itself doesn't add much weight compared to the 600-pound weight limit. Stanleykswong (talk) 09:26, 8 March 2025 (UTC)[reply]

Yes, that works. Just make sure the centre of mass doesn't move between the four readings, or the weight may be redistributed over the scales. PiusImpavidus (talk) 10:02, 8 March 2025 (UTC)[reply]

The redistribution shouldn't affect either total, though, should it? -- Avocado (talk) 13:30, 8 March 2025 (UTC)[reply]

Agreed, the weight distribution between the bed legs should not affect the total weight. Stanleykswong (talk) 13:38, 8 March 2025 (UTC)[reply]

Four is a bad number to use. The problem is if they're all load bearing it might not be stable; weight might shift between corners due to the slightest of shifts, or even due to the scales opposing each other. If you can find a way to use three it should be much more stable. You could place two at corners but a third in the middle of the opposite edge.

This also helps with another problem that bathroom scales are often only approximate. Taking readings off three or four will multiply this error by three or four. No easy fix for this except take readings more than once. Perhaps weigh the bed before and after your human is on it, and if the discrepancy is large also re-weigh your human and average the results. --2A04:4A43:909F:FB44:28A1:3B73:AC99:CE94 (talk) 13:46, 8 March 2025 (UTC)[reply]

I believe your car is likely on four wheels as well, does it have the stability issues you describe?  All four wheels are load-bearing and I believe it is very stable.

I agree with you that most bathroom scales are inaccurate, especially when you compare it to the scales used in hospitals or clinics.   But the typical deviation is only 0.05 to 0.15 kg. Stanleykswong (talk) 14:26, 8 March 2025 (UTC)[reply]

A car doesn't have the problem I describe but a car is a highly engineered device with particular attention paid to balancing load between wheels, keeping all four wheels on the ground as much as is possible, using its suspension.

Many of us have had to deal with a piece of furniture with four legs that doesn't sit stably on all four. Maybe the floor surface is uneven, or its legs. A wooden chair/table on a rustic tiled floor e.g. Typically two opposite legs are always in contact but only one of the other two is at a time, as it wobbles between them. Put springs under both of them and it might oscillate, and that's effectively what you are doing with scales. A three legged item doesn't have this problem, can be stably placed on even a very uneven surface. --2A04:4A43:909F:FB44:24EA:EF2B:7143:1443 (talk) 15:49, 8 March 2025 (UTC)[reply]

If the four scales are identical and the bed is not already wobbly on a flat floor, I don't expect this to be a problem. The relation between the downward force and the vertical displacement of the surfaces of the scales supporting the weight is not linear. If the centre of mass of bed + patient is over the centre of the rectangle formed by the scales, the potential energy is minimized when the springs of all four scales are compressed equally. Even if the bed is wobbly, just use one or two shims under the shorter legs.  ​‑‑Lambiam 19:07, 8 March 2025 (UTC)[reply]

Having the weight on 4 scales instead of 3 leaves one degree of freedom: how much of the weight is on the legs of one diagonal combined and how much is on the legs of the other diagonal combined. It shouldn't change too much under shifts in the centre of mass, but this could be a problem for beds with inconvenient elastic properties. For example, if it's bistable under torsion deformations. Allowing for some elastic deformation of the bed, the distribution gets more equal. If the bed wobbles, the legs in intermittent contact with the ground never carry more than a tiny fraction of the weight.

What could be a serious problem with more than 3 scales is elastic deformation of the floor. When the person taking a reading walks to one of the scales, the floor locally bends down, redistributing the weight away from that scale, leading to a measurement that's too low. This could be an issue if the elastic deformation of the floor is significant compared to that of the scales and the bed. That is, on a wooden floor.

The deviation of the scales would most likely be a systematic error, so taking the same measurement twice won't help. Worse, if all scales are from the same batch, you can expect them to have the same error, so that really adds up. On the other hand, the weight of a person fluctuates over the course of a day by several hectogrammes, so outside special contexts where such factors affecting weight are properly taken into account, measuring a person's weight to an accuracy better than 5 hg is rarely useful.

Alternatively, you could build scales large enough for the entire bed. Something like Sir Bedevere's largest scales will do. Or a weighbridge. My municipal waste dump has one; they weigh your car before and after dumping and charge for the difference.

PiusImpavidus (talk) 19:33, 8 March 2025 (UTC)[reply]

"Worse, if all scales are from the same batch, you can expect them to have the same error, so that really adds up." True, thus I would simply weigh myself on a known accurate scale, before plopping on an unknown one. It works every time. :-) Modocc (talk) 19:49, 8 March 2025 (UTC)[reply]

"What could be a serious problem with more than 3 scales is elastic deformation of the floor.". There could be a number of triggers, for them to find a new stable state. The person on the bed could move, or even depending how sensitive things are just breathe. And unless you have some way of reading them all at once such a shift could completely ruin the readings. Don't forget the ones that might change together are on opposite corners. If you take readings of them in order there could be several seconds during which a shift happens undetected while you are looking at one of the ones that does not change. --2A04:4A43:909F:FB44:683A:7FEE:BE65:E75 (talk) 20:11, 8 March 2025 (UTC)[reply]

Good point. Yes, if you want a person's accurate weight, you have to take readings from different scales at the same time. This can be done by using scales with USB, RS485 or wireless connection and connecting them to the same mobile app or computer program. I don't know if there are any home scales with this kind of connectivity. If not, then you may need to use industrial scales. In this case, rather than purchasing three or four industrial scales, it may be cheaper and easier to simply use a large bed scale, such as Marsden M-955. They're actually a bed with a weight sensor on each of its four legs. Stanleykswong (talk) 20:53, 8 March 2025 (UTC)[reply]

There’s no doubt that a three-legged bed won’t wobble. This can and often is done with beds with four legs, as it is impossible to keep all four legs even. However, this can happen regardless of whether there are scales underneath it.  So, technically, if the bed doesn't wobble without scales underneath it, it won't wobble if the four scales are identical or nearly identical. Stanleykswong (talk) 19:52, 8 March 2025 (UTC)[reply]

Which is what I wrote. However, if the floor itself is not flat or unstable, for example if there is an earthquake while the measurements are done, or the floor consists of spring mattresses, all bets are off.  ​‑‑Lambiam 10:00, 9 March 2025 (UTC)[reply]

Much of the action in this 1986 Australian film involves a truck with a very "army surplus" appearance, that I, a non-enthusiast, have been unable to identify. My copy of the film is of poor quality, possibly ex-VCR, but the vehicle has several distinguishing features: it has one rear axle, so is probably 4x4. The engine hood is shaped from flat surfaces, reminiscent of some GM WWII trucks, and the logo above the radiator appears to be three letters of similar size: most likely ATO or ATC, but the "T" might be a "Y". Notably, it is a cab over design; the driver's door is directly over the front wheel and part of the engine cowling is forward of the front wheels. In the YouTube copy it is first seen at 43:33 and intermittently thereafter.

As the film appears to be based on the documentary The Back of Beyond, it is surprising that the producers did not use an AEC Badger as driven by Tom Kruse, unless these "army surplus" vehicles were more readily available.

IMDb says "The truck seen was actually a 1965 Army Truck. Three trucks were utilized for the production. One of the trucks took six weeks to build due to the number of modifications. One of the trucks had to be converted to diesel so it could drive through water for the river crossing sequences." Doug butler (talk) 12:46, 8 March 2025 (UTC)[reply]

A Truck, Cargo, 2.5 ton GS International No.I Mk III perhaps?

Film makers before the 1990s, esecially if on a low budget, were not very fussy about vehicle accuracy and tended to use what was available as long as it looked about right. A notable example is the use of undisguised US-built postwar tanks standing in for German panzers in Patton (1970). [1] Alansplodge (talk) 13:11, 8 March 2025 (UTC)[reply]

I don't think there can be any doubt. The underlying similarities are overwhelming, and the descriptions tally well with the IMDb entry. Thanks Alan. Doug butler (talk) 19:58, 8 March 2025 (UTC)[reply]

I assume this is a side view of one of the trucks, modified for the film shoot. The protruding bonnet may have been one of the modifications.  ​‑‑Lambiam 18:49, 8 March 2025 (UTC)[reply]

That poster is a great find. I don't know how you do it. Thanks Lambiam. Doug butler (talk) 20:05, 8 March 2025 (UTC)[reply]

Resolved

Our article on Orthohantavirus notes that most species cause chronic, asymptomatic infections in their rodent hosts, and they only produce symptoms upon transmission to humans. Are there any reverse-zoonotic pathogens of any sort that do this, i.e. their natural reservoir is humans, and they don't cause any illness in us, but they can spread to some other species and cause an illness? Reverse zoonosis only covers human illnesses. Nyttend (talk) 20:53, 8 March 2025 (UTC)[reply]

My first thought is yes, probably, but how would we know? And if we did know, how would we know we hadn't caught it from animals in the first place? Shantavira|^{feed me} 09:56, 9 March 2025 (UTC)[reply]

There's an asymmetry here, which is the "animals not having any symptoms" premise cannot possibly be true, especially given the definition of symptom. Symptoms in humans, by contrast, are over-reported. Another issue is, how would you even know if a population of wild squirrels is experiencing a 1% increase in their mortality rate? But an unexplained 1% increase in the human mortality rate would be a catastrophic emergency. Abductive (reasoning) 12:02, 9 March 2025 (UTC)[reply]

Nyttend is doubtless using the looser colloquial meaning of 'symptoms' (experienced by the sufferer), which includes what are more correctly distinguished as signs (visible to an observer), per the linked article.

Who originally gave what to whom is not really an issue if an infection has been ping-ponging between host species for perhaps millennia. There remains the original proposition, that some infections might be sign-and-symptomless in humans but cause illness in an animal species.

Presumably one might be identified by observing some sickness in an animal species, establishing its cause as a particular pathogen, and then discovering that humans harbour and transmit that pathogen without suffering any ill effects. Anthropocentrism seems to have led to little research or publication about such pathogens, but it seems very unlikely that none exist. {The poster formerly known as 87.81.230.195} 94.2.64.108 (talk) 13:53, 9 March 2025 (UTC)[reply]

I'm just relying on what the Orthohantavirus article says: Hantaviruses in their natural reservoirs usually cause an asymptomatic, persistent infection. If you disagree, Talk:Orthohantavirus is the place to discuss it. IP, you're thinking along the same lines as I was. As far as anthropocentrism, I suppose such a disease would be more easily found in species significant to humans, e.g. livestock. Nyttend (talk) 22:10, 9 March 2025 (UTC)[reply]

We have an article at asymptomatic that includes a list (some of which are dubiously asymptomatic to my untrained eye, but it is what it is). You could click through and see if any of them cause illness in animals. I didn't immediately see any obvious candidates, but it's a long-ish list. Matt Deres (talk) 00:08, 10 March 2025 (UTC)[reply]