Wikipedia:Reference desk/Archives/Science/2018 March 21

= March 21 =

Big toe anatomy
I am looking for information of the anatomy of the big toe, but all the pictures and info I can find only show the big toe joint close to the foot, I am looking for info on the first big toe joint that bends close to the nail, what is it called? I am also wondering if this is an actual joint with cartilage or just bones.--User777123 (talk) 04:04, 21 March 2018 (UTC)
 * That joint has a synovial membrane. The end bone has a double concavity. The bone is called Pedal distal phalanx 1. The big toe has no middle phalanx. There are collateral ligaments on either side. It is connected to plantar ligament connected to articular capsule. Info from Cunningham's Text-Book of Anatomy, 9th ed, by James Couper Brash. A picture of the bone is here: http://www.eskeletons.org/boneviewer/nid/12537/region/feet/bone/pedal_distal_phalanx_1 . It connects to  Extensor hallucis longus muscle. Graeme Bartlett (talk) 07:40, 21 March 2018 (UTC)


 * I'll add that the joint closest to the nail is called the interphalangeal joint of the hallux (aka digit 1 of the foot). -- Flyguy649 talk 22:13, 22 March 2018 (UTC)

Weighing scale
Can anyone please point me to a weighing scale which can measure mass up to 1 kg (or, if not, then at least up to 500 g), with the highest possible precision (if possible, ±10 mg or better, but if not, then the best available) and with the greatest possible accuracy? I bought one which meets these specs (or so I thought) on eBay, but it turned out to be a piece of junk -- just today I tried to weigh a 2 L beaker full of water, and it showed the weight as 1410 kg (and that right after calibration!), and as far as smaller weights (like empty beakers, or even a 1 L beaker half full of alumina powder), it remains stubbornly stuck at 0.00 g! 2601:646:8E01:7E0B:0:0:0:9ED6 (talk) 06:36, 21 March 2018 (UTC)
 * It appears that 2kg broke your 1kg limit scale. Anyway you want accuracy to 1 part in 100,000. You will have to take into account air buoyancy, which will vary at your precision with temperature and pressure.  So you will need to weigh in a vacuum or have extra compensation. I can see examples that should be a good enough quality here: https://www.instrumentchoice.com.au/instrument-choice/other-meters/digital-scales-1/precision-and-analytical-balances and another here: http://www.scaleshop.com.au/adam-nimbus-nbl-e/ . Some of the scales here https://www.austscientific.com.au/product/balances/ have compensation for pressure and temperature (but I did not see humidity) and also prevent electric fields that also affect measurements. But they mostly do not meet your requirements for maximum. Graeme Bartlett (talk) 08:10, 21 March 2018 (UTC)
 * Actually, all 3 of them are good, but far too expensive -- I guess I'll have to settle for using 2 scales, one for weighing small amounts of chemicals (up to, say, 100 g) with high precision, and another one for weighing large amounts (up to 1 kg, preferably higher) with rather lower precision. 2601:646:8E01:7E0B:0:0:0:9ED6 (talk) 08:52, 21 March 2018 (UTC)
 * I'm slightly confused, did you scale support up to 1kg or did it supposedly support a higher weight limit? If it was only up to 1 kg and you tried to weigh something heavier like a 2L beaker full of water, it's not completely surprising it would break perhaps permanently as Graeme Bartlett has said. With the cheap scales I've bought from AliExpress I've generally gotten away with a fair amount of abuse. But if I was buying a expensive high precision scale from a proper manufacturer, I wouldn't be testing the limits especially to such an extreme. You can only go so far until you actually damage the strain gauge or whatever is used or something else. (In any case, for something from eBay particularly if it's new and from an uncertain manufacturer, you should always consider the possibility it may be DOA. So test it properly when it first arrives and report it to the seller if it is so you can get a replacement.) Anyway I have seen ultra high precision, supposedly 1 mg scales, supporting up to 1 kg and with an enclosed measuring surface on AliExpress e.g. www.aliexpress .com/item/1kg-0-001g-1mg-electromagnetic-scale-calibration-weights/32810440445.html. And high precision, supposedly 10 mg, scales supporting up to 1kg are very common both the cheap dime a dozen ones which don't even have an enclosed measuring surface (so you know that at a minimum, the accuracy is very questionable) e.g. www.aliexpress .com/item/1PC-Professional-Pocket-1KG-0-01G-Scale-Digital-Jewelry-Precision-Balance-Weighing-Scale-With-Backlight-Keyboard/32819638592.html and those that do e.g. www.aliexpress .com/item/New-APTP457B-Precision-Jewelry-gold-food-weighing-counting-kitchen-scale-1KG-x-0-01g-Laboratory-analytical/32622805989.html.  I'm not suggesting you get these if you actually need these for an important reason (I do actually use a 0.01g scale from AliExpress/eBay but only really for fun, e.g. cooking, in fact 0.1g would do I mostly want something more than 1g and it's a choice between 3kg or so 0.1g and 1kg or so and 0.01g). But these suggest to me you should be able to get one from a decent manufacturer. As GB has said, if you actually need that level of precision you'll need to consider carefully compensation measures.  Nil Einne (talk) 08:36, 21 March 2018 (UTC)
 * For the record, the scale I have is rated to measure weights up to 3 kg (in fact, the calibration weights are 2 kg in all) -- therefore, my weighing the beaker could not possibly have anything to do with the malfunction (and in any case, it was stuck at 0 for smaller weights even before I weighed the beaker). 2601:646:8E01:7E0B:0:0:0:9ED6 (talk) 08:42, 21 March 2018 (UTC)
 * Does it have a zero button to re-zero it with no mass on the platform? Graeme Bartlett (talk) 09:58, 21 March 2018 (UTC)
 * Your description sounds like it was DOA. Even the best brands have this, so I wouldn't conclude from a single instance that the scale model is no good. If it sold as a new & working scale, the seller should set this right especially if they are a commercial seller. Nil Einne (talk) 10:40, 21 March 2018 (UTC)
 * What is "DOA"? 92.8.216.101 (talk) 13:41, 21 March 2018 (UTC)
 * The first sense at DOA&mdash;that is, dead on arrival. In the context of manufactured products, it means that the item was critically defective as-delivered. TenOfAllTrades(talk) 15:24, 21 March 2018 (UTC)


 * To get within 10 mg you want a jewelers' scale, which typically goes to 100g at the most. You can buy them in head shops among other places.  You might be better off with a lab scale that has a draft shield; i.e., after putting your sample on the scale, you put a transparent box over the whole scale to prevent air currents in the room from disturbing the measurement.  Digital scales measure weight using strain gauges which can be damaged if you put too much weight on them, so yes your scale might have gotten messed up if you overloaded it.  Also, obviously, they measure force (F=M·g) rather than mass.  If you really want to measure mass directly, you want a balance-type scale.  I like typing "Ohaus" into craigslist search (sfbay.craigslist.org) just to see pictures of nice old ones, though I don't feel likely to buy one). 173.228.123.121 (talk) 19:56, 21 March 2018 (UTC)

Reflector telescope design
I'm looking for a reflector telescope design where the secondary mirror is offset out of the telescope tube. My motivation is (1) aperture control and (2) better bokeh. thanks! --Masatran — Preceding unsigned comment added by 117.251.229.98 (talk) 07:33, 21 March 2018 (UTC)
 * I think they're called off-axis reflectors. A curved spider in an on-axis reflector would get rid of the diffraction spikes at least (Maksutovs have a small secondary mirror but have a corrector plate that can't be 100.000% transparent). Sagittarian Milky Way (talk) 08:02, 21 March 2018 (UTC)

How long after last frost before lawns need mowing?
What temperature do lawns consider a frost? 32? 30? 28? 107.77.173.12 (talk) 17:56, 21 March 2018 (UTC)
 * The growth rate of the grass depends on too many factors to give a simple answer - temperatures, moisture levels, grass species, soil nutrient levels, sunlight levels. If it stays dull, and just above freezing, the grass will grow a lot more slowly than if the temperature shoots up very quickly and there is plenty of sunshine. Wymspen (talk) 18:18, 21 March 2018 (UTC)


 * Today, many people cut their grass too short. If you keep it no shorter than 2 inches (and I don't mean bowling greens but garden lawns). That too, will help prevent weeds colonizing (so avoid the need for lawn weed treatments). When in the spring,  the grass grows to 3 inches,  mow it on a day when there is no 'frost'. It is only when the ground is frozen that damage is done because grass grows from the base and any physical trauma will damage the leaf buds. --Aspro (talk) 19:11, 21 March 2018 (UTC)


 * Another thing to potentially consider 93.136.50.38 (talk) 00:29, 22 March 2018 (UTC)


 * Interesting question. I went ahead and asked on https://gardening.stackexchange.com/q/37656/13670 and was pointed to a UK news article differentiating between air frost and ground frost. The basic answer I got was that you can mow when the grass needs it (e.g. is >2inch tall) and it and the ground is not frozen. Generally the ground only freezes during extended day and night sub-freezing temperatures, similar to pipes freezing; it isn't immediate but takes extended cold temperatures, with shorter time required the colder it gets. A 32F night can result on frosty surfaces but the ground would not be necessarily be frozen. If the ground is not frozen and the grass itself doesn't have frost on it, the grass can handle a mowing, but if the ground is frozen or the grass itself has frost on it you're better off leaving the grass alone as the disturbance of cutting or even just bending the frosted plant material could injure it into the growing season. Cr0 (talk) 00:33, 22 March 2018 (UTC)