Monthly Archives: March 2018

Adding anticipation to automatic transmission

Some of the downsides of automatic transmission in cars are that it does not anticipate hills or overtaking, and does not respond to slippery conditions appropriately. The technology that could enable the transmission to anticipate hills or overtaking is already available and incorporated in some cars, namely GPS, maps and sensors that look ahead of the car. If the map data includes altitude, then the location and movement direction of the car on the map predicts the slope that the car will be on in the near future. This information could be sent to the automatic transmission to enable it to shift gears in anticipation of a hill. A forward-looking sensor that has a range of a few hundred metres can also see a hill if the road does not curve too much. The sensor data could also be sent to the transmission. Similarly, a sensor could detect the nearing of the car in front and shift to a lower gear to prepare to accelerate for overtaking.
Slippery conditions can be predicted using the car’s thermometer, perhaps with the addition of a humidity sensor, or detected using a wheel slip sensor. This information could also be sent to the computer controlling the automatic transmission, to prevent it from spinning the wheels too fast when there is little grip. The GPS or forward-looking sensor could also tell whether the car is moving relative to the landscape. Comparing the movement data with the wheel spinning speed reveals whether the wheels are slipping.

Speculative etymology of the word “partner”

I was confused when I first encountered the word “partner” in the context of referring to a spouse or the person one is in a romantic relationship with. I thought: “What partner? Business partner? Tennis partner? Oh, sex partner – that’s where the reference to partner comes from.”
A similar speculative etymological derivation can be applied to the US slang phrase “hook up”, which means to start a romantic relationship. The phrase arose to describe a situation in which a “hook” goes up something, specifically someone’s bottom.

Gender equity either on paper or by forcing people to change research fields

Suppose that a university employs roughly equal numbers of men and women overall, but the proportions of the genders differ across research fields, or across research and administration, and the university wants gender equality within each subfield. Using the narrowest definition of a research field, each field has either one or zero people, so in the smallest fields, gender equality is impossible. From now on, the focus is on fields or administrative units that have at least two people.
Gender equity can be achieved on paper by redrawing the administrative boundaries or redefining research fields. A simple algorithm (not the only possible algorithm) is to form pairs of one male and one female employee and call each such pair an administrative unit. Larger units can be formed by adding many male-female pairs together. If the numbers of men and women are not exactly equal, then some single-gender pairs will be left over, but most administrative units will have perfect gender equality.
The same idea can be used less radically by reassigning people who do interdisciplinary work and could plausibly belong to multiple research fields. Each person who is „between” fields gets assigned to the field that has a smaller fraction of that person’s gender. This increases gender equality in both the field that the person joins and the field that the person left. The field with a bigger surplus of that person’s gender loses one of that gender, and the field with a smaller surplus gains one.
Other than reassigning people or redrawing administrative boundaries, gender equity requires inducing people to change their research fields. To some of my colleagues, directing researchers to change their area is ideologically unacceptable. However, if equity is the goal and people’s field change is necessary to achieve it, then several methods can be used. The inducements can be softer or harder. A hard inducement is a hiring policy (and job ads) that restrict hiring to only one gender. The same can be done with promotion and retention. If this policy was explicitly stated to everyone, then it would become more effective, and also more acceptable to people than when they are surprised with it upon applying for promotion.
Soft inducements consist of hints that one gender is preferred, which are usually stated in political doublespeak like „we are committed to equity” or „we are an equal opportunity employer”. If many more candidates of one gender apply, then giving all candidates an equal opportunity of getting hired does not result in equal proportions of men and women employed. I am in favour of clear guidelines and transparency, for example of explicitly stating in job ads and promotion policies that the underrepresented gender is preferred, and which gender is currently underrepresented. Clearly telling people that switching fields is good for their career is likely to have a bigger effect than the currently used hints.
It may be easier to shift the research areas of people who are earlier in their careers. Encouraging more young people of a given gender to go to an area where their gender is underrepresented is one way of inducing them to change their field (relative to their preference).
Current equity policies are focussing almost exclusively on the inflow of employees. Gender balance can also be improved by managing the outflow, for example by offering early retirement schemes to one gender, or expanding these to a wider age range for one gender. If there are gender differences in the propensity of accepting certain inducements to leave, then the same inducements can be offered to both genders (seemingly gender-neutrally), with the desired result that one gender exits more.

Laplace’s principle of indifference makes history useless

Model the universe in discrete time with only one variable, which can take values 0 and 1. The history of the universe up to time t is a vector of length t consisting of zeroes and ones. A deterministic universe is a fixed sequence. A random universe is like drawing the next value (0 or 1) according to some probability distribution every period, where the probabilities can be arbitrary and depend in arbitrary ways on the past history.
The prior distribution over deterministic universes is a distribution over sequences of zeroes and ones. The prior determines which sets are generic. I will assume the prior with the maximum entropy, which is uniform (all paths of the universe are equally likely). This follows from Laplace’s principle of indifference, because there is no information about the distribution over universes that would make one universe more likely than another. The set of infinite sequences of zeroes and ones is bijective with the interval [0,1], so a uniform distribution on it makes sense.
After observing the history up to time t, one can reject all paths of the universe that would have led to a different history. For a uniform prior, any history is equally likely to be followed by 0 or 1. The prediction of the next value of the variable is the same after every history, so knowing the history is useless for decision-making.
Many other priors besides uniform on all sequences yield the same result. For example, uniform restricted to the support consisting of sequences that are eventually constant. There is a countable set of such sequences, so the prior is improper uniform. A uniform distribution restricted to sequences that are eventually periodic, or that in the limit have equal frequency of 1 and 0 also works.
Having more variables, more values of these variables or making time continuous does not change the result. A random universe can be modelled as deterministic with extra variables. These extras can for example be the probability of drawing 1 next period after a given history.
Predicting the probability distribution of the next value of the variable is easy, because the probability of 1 is always one-half. Knowing the history is no help for this either.

Vaenlasekuju suurendab ustavust

Kõik diktatuurid püüavad oma elanikkonda veenda, et riik on ümbritsetud vaenlastest ja vaenlased on ka sisse imbunud. Propaganda spioonide ja diversantide kohta annab õigustuse suvaliste inimeste represseerimiseks – tuleb vaid sisevaenlase silt külge riputada. Välisvaenlase kuju on vaja selleks, et hoida elanikke piiramismentaliteedis ja juhtkonnale ustavana. Kriitikat režiimi aadressil ja püüdlust muudatustele vaigistatakse hoiatusega, et see nõrgestab riiki välisvaenlaste ees. Nõrgestamishirm on osalt põhjendatud – segadusteaeg riigis on alati sissetungi lihtsustanud.

Vaenlasekuju loomine pole päris sama, mis naaberriikide halvustamine ja diktatuuri ülistamine. Diktatuuri suhtelisest elustandardist vale mulje jätmisega püüab propaganda tekitada uskumust, et diktatuuris võib inimestel küll halb olla, aga mujal on veel halvem. Sellega hoitakse elanikke välismaale pagemast. Naaberriike halvustades jäetakse mulje, et need on vaesed ja viletsad, aga vaenlasi seinale maalides püütakse ohtu suureks puhuda ja väita, et naaberriikidel on palju vahendeid ja võimalusi kahju tekitamiseks. Naaberriikide hea varustatus viitab aga kaudselt nende rikkusele.

Paistab, et on mingi psühholoogiline mehhanism, mis paneb inimesed ohu korral juhte rohkem toetama. Hirm suurendab ustavust omadele. Seda mehhanismi kasutatakse laialt, mitte ainult diktatuurides.

Igasugused võistlused ja võrdlused riikide vahel, olgu siis spordis, laulus või statistilistes näitajates, tunduvad tõstvat patriotismi. Ka Eesti ajakirjanduses tekitavad riikide võrdlused ettevõtlusvabaduse või inimarengu indeksi põhjal rohkesti vastukaja. Hea tulemuse korral taotakse endale vastu rinda, halva korral leitakse vabandusi või teisi valdkondi, kus ollakse tublid. Spordi puhul on sellist käitumist veel rohkem, kuna valdkond on emotsionaalsem.

USA ülikoolid kasutavad rivaalitsemist spordis tudengite sideme tugevdamiseks ülikooliga, et hiljem oleks lihtsam vilistlastelt annetusi kätte saada. Just põhikonkurendiga toimuvate võistluste ajal on toetus omadele kõige suurem, ja suurvõistlus paistab olevat kõige intensiivsema annetustenurumise aeg. Võistlemisest saavad kasu kõigi osalevate ülikoolide juhtkonnad, sest see suurendab annetusi kõigile. Suur ressursikulu tudengispordile (staadionite ehitus, võistkondadele eraldi võimlad, stipendiumid sportlastele) on seletatav annetustega, mida sport sisse toob.


Miks soovitab Warren Buffett eraisikule osta-ja-hoia strateegiat ja laiapõhjalisi madala haldustasuga indeksfonde? Madal haldustasu on loogiline, sest haldustasu vähendab investeeringu tulumäära. Indeksfondid ei tee midagi keerulist ja kallist, mis nõuaks kõrget haldustasu. Need järgivad turu keskmist tootlust. Mida laiapõhjalisem (mida suuremat osa maailma aktsiaturgudest hõlmab), seda väiksem on tootluse dispersioon sama keskmise tootluse juures. Ehk sama tulususe juures on risk väiksem. Osta-ja-hoia strateegia tähendab fondiosakute ostmist säästude tekkimisel ja osakute hoidmist kuni raha vaja läheb, näiteks pensionieani. See strateegia väldib spekulatiivset kauplemist (ostu-müüki lootuses, et aktsia hind tõuseb või langeb). Spekulatiivne kauplemine vähendab tulusust kahel põhjusel: tehingutasud ja väheminformeeritud kaupleja turukeskmisest madalam varakasv. Tehingutasude seos kauplemisega on ilmne. Eraisik on suurtest kauplemisfirmadest vähem informeeritud, sest finantsinfo kogumisel, majandusprognooside tegemisel, arvutusvõimsuse ostmisel, jne on mastaabisääst. Ettevõtte kasumi ja majanduse kasvu prognoosimise kulu on sama, ükskõik kas kaubelda ühe või miljardi aktsiaga, aga tulu (või kahjum) miljardi aktsia kauplemisest on miljard korda suurem ühest aktsiast. Nii on ratsionaalne investeerida aktsia tulususe ennustamisse rohkem siis kui kaubeldakse suuremat kogust. Suured kauplemisfirmad ostavad ratsionaalselt endale rohkem infot kui palju väiksemat summat investeeriv eraisik. Infot ostetakse nii seaduslikul kui ebaseaduslikul viisil. Seaduslikud on statistika kogumine, aastaaruannete lugemine, prognooside tegemine. Ebaseaduslikud on siseinfo ost, tööstusluure, turumanipulatsioon. Poolseaduslik on lobitöö enda omatavate firmade kasuks. Kõigis neis on eelis suurtel kauplemisfirmadel.
Osaliselt võib suurfirmade eelise neutraliseerida see, kui teised turuosalised nende kauplemistegevuse kohta signaale saavad, näiteks börsil suurt ostukogust näevad. Siis saavad teised turuosalised suurfirmat jäljendada, mis tõstab hinda ja vähendab suurfirma kasumit ostmisest. Antud näites sõidavad teised turuosalised jänest suurfirma kogutud infol. Eriti suur probleem on see suurfirma jaoks siis, kui teised turuosalised (kõrgsageduslikud kauplejad) oma ostuorderi suurfirmast kiiremini börsile saata saavad. Siis saavad ettejõudjad ära võtta kogu suurfirma kasumi (kui ostavad piisavalt suure koguse), ehk suurfirma kaotab kogu kasu info hankimisest.
Samas, kui teised turuosalised suurfirmat jäljendavad, loob see suurfirmale võimaluse turumanipulatsiooniks. Selle manipulatsiooni kuulus näide on Rothschildi kauplemine Waterloo lahingu järel. Teised teadsid, et Rothschildil on kiiremad kullerid ja ta saab lahingu tulemuse enne teisi teada. Rothschild teadis, et teised seda teadsid, nii et ta teeskles lahingu järel Londoni börsil müümist, mis pani ka jäljendajad müüma. Aga varjatud käsilaste kaudu Rothschild hoopis ostis, ja ostis salaja rohkem kui nähtavalt müüs. Nii sai Rothschild oma avaliku müügi jäljendajate aktsiad odavalt kätte ja jäljendajad said suure kahjumi.

Kui mõni eraisik suudab mõne väärtpaberi hinda pikka aega turust paremini ennustada, siis saaks see eraisik teenida suurema kasumi kui ainult enda varaga kaubeldes. Nimelt võiks see eraisik luua oma investeerimisfirma ja võtta haldustasu teiste raha investeerimise eest turukeskmisest kõrgema tulususega.

Paljude sarnaste indeksfondide olemasolul võiks mugavuse ja likviidsuse huvides valida börsil kaubeldava indeksfondi, mille osakuid saab osta ja müüa nagu aktsiaid, ehk ei pea eraldi fondi astumise või väljaastumise lepinguid sõlmima.

Ülaltoodud argumendid on teoreetilised, aga investeerimisstrateegia kohta on ka palju empiirilist teadustööd, näiteks Grinblatt ja Keloharju (2000) Soome andmetel, ja Barber ja Odean (2001). Empiirilised faktid võtab hästi kokku ühe artikli pealkiri: „Trading is hazardous for your wealth”, ehk kauplemine kahjustab teie vara. Selle artikli põhitulemus on, et need eraisikud, kes spekulatiivselt kauplevad (tihti ostavad ja müüvad), saavad aktsiaturult madalamat keskmist tulu kui need, kes ostavad ja hoiavad.
Eelnevaga seotud teoreetilised tulemused on mittekauplemise teoreemid (no speculative trade theorems), mis ütlevad, et riskikartlikud või riskineutraalsed otsustajad, kes on ratsionaalsed ja kelle ratsionaalsus on neile kõigile üldteada, ei kauple spekulatiivselt. Tõestuse idee on järgmine. Ratsionaalne ostja, kes teab, et teine ratsionaalne kaupleja on valmis müüma, teeb teise müügivalmidusest järelduse, et aktsia väärtus on väiksem kui müügihind, seega väiksem kui ostuhind, seega on aktsia ostmine kahjumlik. Sümmeetriliselt, ratsionaalne müüja järeldab ostja ostuvalmidusest, et aktsia on väärt rohkem kui müügihind, seega ei tasu seda müüa.
Ratsionaalsed kauplejad, kes arvavad, et teised on riskiarmastajad või ebaratsionaalselt kauplemishimulised, võivad kaubelda. Spekulatiivne kauplemine võib toimuda ka siis, kui ratsionaalsed turuosalised arvavad, et teised arvavad, et teised on riskiarmastajad või ebaratsionaalselt kauplemishimulised, või et teised arvavad, et teised arvavad, et teised on riskiarmastajad või ebaratsionaalselt kauplemishimulised, või…
Mitte igasugune kauplemine pole spekulatiivne. Kui ühel inimesel on hetkel sääste, mida ta ei kasuta, aga teine inimene vajab hetkel sularaha, siis kui esimene ostab teise aktsiad, siis mõlemad võidavad. Hiljem võib jälle esimene raha vajada ja teisel raha üle olla, nii et teine ostab esimese aktsiad. Sarnane mõlemapoolne kasu võib tekkida muude varade kauplemisest, näiteks üks inimene vajab autot nädalavahetustel, aga teine tööpäevadel, nii et iga reede õhtul ostab esimene teiselt auto ja igal esmaspäeva hommikul müüb auto teisele tagasi. See on üks viis autojagamist organiseerida, aga levinum viis on, et üks inimene on omanik ja rendib autot teatud aegadel teisele.

Taking your own fingerprints

Some jobs, visas, etc, require a criminal record check from the FBI, which requires sending the FBI your fingerprints. Where you live, it may be difficult to find a professional who will take your fingerprints on an FBI-approved fingerprint card. But no problem, it is quite feasible to take your own fingerprints.
Supplies needed:
1. Scrap paper to practice on
2. Printouts of the FBI fingerprint card on standard office paper (5-10 copies, because you will make mistakes)
3. Ink pad from a stamp (with some black or blue ink in it). For most brands of stamps, the internet has instructions on how to slide the ink pad out.
4. Piece of smooth rubber a little larger than a fingertip, e.g. a piece of bicycle inner tube, a piece of unlubricated condom, or a rubber ball about 5 cm in diameter
5. Paper towels or tissues for wiping ink from fingertips
6. Stick of glue for gluing paper
7. Small sharp straight scissors, or a razorblade and a smooth cutting board, for cutting paper
8. Large envelope for mailing the fingerprint card to the FBI without folding it. Postage stamp(s).

The piece of smooth rubber is for painting the ink of the stamp pad onto the ridges of the fingerprints. Just dipping the fingers in ink or touching them to the stamp pad will put ink in the troughs of the fingerprints as well. Too inky fingers will create a uniform splotch on the paper, not the lines and whorls of a fingerprint. Also, if the stamp pad holds the impression of the writing on the stamp, then the fingers will get that writing on them as inkless areas.
The ink should not be quick-drying, e.g. alcohol-based from a marker pen. This will dry on warm fingertips before the finger reaches the paper. The ink must be liquid, not the paste from a ballpoint pen, because the paste sticks to the fingertip in small chunks. These will create uniform dark splotches on the paper, with the adjacent areas blank white. The ink used in stamp pads is good.
With inky fingers, it is easy to get ink stains on the table or anything else within reach, so the paper towels or tissues should be held ready to clean the ink up while it is still wet.
1. Read the FBI’s online instructions for taking legible fingerprints (, the Guidelines for Preparation of Fingerprint Cards ( and the Capturing Legible Fingerprints poster (
2. Lightly rub the bulging side of the piece of rubber on the stamp pad to coat it with an even thin layer of ink. Then lightly paint the ink on one fingertip, the first priority being to coat all the ridges from the crease of the first joint to the nail and from one side of the nail to the other. The second priority is to avoid coating the troughs of the fingerprint. Some ink in the troughs is unavoidable, but minimising it will make the print clearer.
3. Roll the fingertip on the scrap paper from nail to nail, like the FBI instructions say. Compare the result to the Capturing Legible Fingerprints poster. The goal is to get a roughly rectangular imprint with the ridges and troughs of the fingerprint visible. Empty spots on the fingerprint indicate too little ink, inky splotches indicate too much. Lightly pressing the second joint of the finger down with the thumb and forefinger of the other hand may help, or alternatively holding the tip of the nail down with the thumb and forefinger of the other hand. Practicing repeatedly with the same finger helps. The ink on the fingertip needs renewing from time to time. If there is too much ink on the fingertip, rolling it on the scrap paper will reduce the amount.
4. Estimate how much ink on the fingertip leaves the best print. If the first roll after inking a finger always creates splotch, estimate how many rolls on the scrap paper are needed (without renewing the ink) to make the fingerprint legible.
5. Once the fingerprints on the scrap paper are looking good, use the same amount of ink and pre-rolls to put the same finger’s print on all the FBI fingerprint cards.
6. Wipe this finger clean of ink.
7. Repeat points 2-6 with each finger. When reaching the thumbs, also put their flat impressions on the fingerprint card (flat thumb impressions require less practice). Doing one finger at a time minimises ink stains on the fingerprint card and the furniture, and gives practice for each finger just before that finger’s print is taken.
8. Ink the four fingers of one hand and practice taking the four-finger flat impression a couple of times. Then put the four-finger impression on all the fingerprint cards. Clean the fingers. Repeat with the other hand.
9. Choose the fingerprint card with the largest number of clear fingerprints. It doesn’t matter how bad the unclear prints on the card are – these will be covered in the next step.
10. For each unclear print on the chosen card, pick the clearest print of the same finger from the remaining cards. Cut out that fingerprint, following the edges of the box it is in. Glue the cutout over the unclear print on the chosen card, making sure all four corners of the cutout are glued down. Hopefully you only need to cut and glue at most 3 prints.
11. Fill out the form at the top of the fingerprint card with black or blue pen, as the instructions say. The required codes for hair and eye colour, etc, can be found in the Guidelines for Preparation of Fingerprint Cards.
12. Without folding the fingerprint card, put it in the envelope together with the printout of the email confirmation of paying the appropriate fee on the FBI website. Address the envelope correctly and mail it. From Australia, sending the A4 envelope to the FBI using regular mail cost under 3 AUD in 2018. In my case, the pdf of the criminal record check was accessible from the FBI’s website less than two weeks after mailing my fingerprint card.

How superstition grows out of science

Priests in Ancient Egypt could predict eclipses and the floods of the Nile by observing the stars and the Moon and recording their previous positions when the events of interest happened. The rest was calculation, nothing magical. Ordinary people saw the priests looking at the stars and predicting events in the future, and thought that the stars magically told priests things and that the prediction ability extended to all future events (births, deaths, outcomes of battles). The priests encouraged this belief, because it gave them more power. This is one way astrology could have developed – by distorting and exaggerating the science of astronomy. Another way is via navigators telling the latitude of a ship using the stars or the sun. People would have thought that if heavenly bodies could tell a navigator his location on the open sea, then why not other secrets?
Engineers in Ancient Rome calculated the strength of bridges and aqueducts, and estimated the amount of material needed for these works. Ordinary people saw the engineers playing with numbers and predicting the amount of stones needed for a house or a fort. Numbers “magically” told engineers about the future, and ordinary people thought this prediction ability extended to all future events. Thus the belief in numerology could have been born.
When certain plants were discovered to have medicinal properties against certain diseases, then swindlers imitated doctors by claiming that other natural substances were powerful cures against whatever diseases. The charlatans and snake oil salesmen distorted and exaggerated medicine.
Doctors diagnosed diseases by physical examination before laboratory tests were invented. Thus a doctor could look at parts of a person’s body, tell what diseases the person had, and predict the symptoms that the person would experience in the future. Exaggerating this, palm readers claimed to predict a person’s future life course by looking at the skin of their palm.
In the 20th century, some medicines were discovered to be equally effective at somewhat lower doses than previously thought. Then homeopathy exaggerated this by claiming that medicines are effective when diluted so much that on average not a single molecule of the drug remains in the water given to the patient.
In all these cases, superstition only adds bias and noise to scientific results. Science does not know everything, but it is a sufficient statistic ( for superstitious beliefs, in the sense that any true information contained in superstition is also contained in science. Nothing additional can be learned from superstition once the scientific results are known.

Miks riigid rahastavad sporti

Enamik riike rahastab oma tippsportlasi. Põhjendusi pakutakse kolme liiki: riigi reklaamimine välismaal, patriotismi kasvatamine kodumaal ja rahvatervise arendamine. Kõik need põhjendused on kahtlased. Ma ei usu, et potentsiaalsed investorid ja turistid lähevad riiki sellepärast, et on näinud selle riigi sportlasi võistlusi võitmas. Kui sportlasel on rahvusvaheline fännklubi, siis võibolla selle liikmed lähevad sportlast tema kodumaale vaatama. Aga selliseid sportlasi on vähe ja fännide sissetoodud raha vist ei kata riigi poolt keskmise sportlase sponsoreerimise kulu.
Kas spordivõidud kasvatavad patriotismi? Seda peaks saama andmete põhjal üsna hästi mõõta, sest võidud on avalikud ja suuresti juhuslikud. Ma ei usu, et keegi toetaks oma riiki oluliselt rohkem, sest kodumaised sportlased võidavad. Kui toetavad, siis kas see toetus koos ülalmainitud reklaamiga välisriikides õigustab spordi sponsoreerimise kulu?
Rahvatervis on kõige levinum tippspordi toetamise argument. Olümpia korraldamine igatahes rahva sporditegemist ei kasvata. Arvan, et mõju tavainimeste sporditegemisele puudub või on pisike ka muul tippspordil. Rahva tervisesporti peaks toetama otse, mitte tippsporti sponsoreerides kaudselt.
Kui tippsport suunab rahvast spordiga tegelema, siis tõenäoliselt sama spordialaga, milles antud riigi sportlane hiljuti võitis. Rahvatervise osas tekib küsimus, kas see spordiala parandab kokkuvõttes tervist, ehk kas positiivne mõju tervisele kaalub üles vigastused (vt ka „Spordiala valiku kriteeriumid”). Tervet rahvast poksi või ameerika jalgpalliga tegelema suunata ma küll ei tahaks, sest nendest saadud ajukahjustused on märgatavad ja meditsiiniliselt tõestatud. Keskmiselt tervist kahjustavaid spordialasid riik toetada ei tohiks.
Tõenäoliselt on spordi toetamise põhjus sama, mis gladiaatorivõitluste toetamisel Vana-Roomas: rahvale tsirkuse pakkumine. Valitsus rahastab sporti, et enda populaarsust suurendada. Sama põhjus seletab ka kunsti rahastamist. Rahastuse vähendamisel hakkaksid rahva hulgas populaarsed sportlased ja kunstnikud valitsuse vastu protestima.

A sewing machine design

Needle shaped like a helix, positioned horizontally. The needle can be held in place by four rollers around it with axes parallel to the axis of the helix and magnets that prevent the helix from moving forward or back along its axis. Another way is to use two rollers above the helix and a magnet above these. The needle is rotated around the axis of the helix by the rollers, which touch it.
As the helix rotates, the corkscrew motion makes the point of the needle go into and out of cloth like a curved surgical needle. The two-roller setup is convenient if access to the other side of the cloth is restricted, e.g. when sewing the lining of a garment closed.
An advantage over the current sewing machines is the simplicity and the need for only one thread per seam, not two threads, one of which is restricted in length because it is on a bobbin. For long seams, the single-thread design has the advantage of dispensing with the bobbin. Long seams are usually simple (hemming curtains, bedsheets), not zigzag or some fancy design, so the limited seam design options with the helical needle are not a big problem.
The problem is that towards the end of a long seam, a long thread needs to be pulled through the entire seam behind the needle. The friction gets large. The thread is not relatively straight, but in a “spiral binder” seam, which bunches the cloth.