Do you remember the little girl from the fairy tale, Thumbelina? Ever thought of the origin of her name? Let's talk about it.
About the word "inch"
Translated from Dutch, the word "inch" means "thumb." This is a measure of length equal to the width of the thumb of the average person (though some claim that this is the length of his upper phalanx). But, no matter what part it is, it turns out that Thumbelina is a girl the size of a finger.
By the way, in the fairy tale epic another hero of the same size is known. It turns out that our beloved Boy-s-Finger, too, could, by analogy, be called Thumbelina. A joke, of course. However, people have different fingers, so still I would like to clarify: how many mm in an inch?
About the size of an inch
Determining what an inch in mm is is not so simple. The fact is that this unit, which is already hundreds of years old, has repeatedly changed even within the same system of measures, not to mention different ones. The Vienna inch was 2.6340278 cm, or 26.3 mm; in Spain, the local inch (pulgada) was 23.2 mm; in Mexico, where it was also called pulgada, the size of an inch in mm was approximately 23.3.
This list can be replenished almost ad infinitum. Each of the German lands had its own, distinct from the others, type of measure of length mentioned: Baden, Bavarian, Saxon and Prussian, as well as an inch of the Rhine Union. In the Ostsee provinces, respectively, there were Courland, Riga and Revel. In the territory of the Polish-Lithuanian Commonwealth there existed Old Polish and Novopolitan inches, as well as Wroclaw, Breslav, Silesian, old Lithuanian. France had its own measure of length. There were similar units even in Japan and China. So, 1 inch (Chinese inch) in mm was 33.3. There is also the so-called Vidicon inch, most often used when measuring the matrix of a digital camera. It is equal to 16.93 mm.
About the Metric Convention and the Metric
On May 20, 1875, in Paris, in the building of the French Ministry of Foreign Affairs, the so-called Metric Convention - a treaty designed to ensure uniformity of international metrological standards. Russia also joined this agreement - on behalf of the emperor, the contract was signed by the embassy adviser Okunev. The adoption of the convention served as an important impetus to the development of the metric system of measures and the beginning of the development of standards for meter and kilogram. Later, the basic units were introduced in the fields of electricity and optics. At present, more than 50 states, including all the most industrialized ones, are attached to the Metric Convention.
Two important points. First: an inch is an obsolete unit that has nothing to do with the metric system at all. Moreover, the OIML (International Organization of Legal Metrology) strongly recommends its speedy withdrawal from circulation where it is still used for measurements (the reason, I think, is understandable). The second remark. The largest and most developed country in the United States, although it has signed the Metric Convention, still does not consider it mandatory to use the metric system of measures. Inch is widely used as a local unit of measure, which, in the rest of the world, seriously impedes adherence to OIML recommendations.
About English inch
So what is this unit all the same, how to express 1 inch in mm? At present, when referring to this term, as a rule, we mean the English, or imperial measure of length. Its value has also repeatedly changed, but since 1958, the conversion of inches to mm will give a result of 25.4 per unit. So the size of our fairy-tale characters would now be 2.54 cm. Indeed, crumbs!
By the way, in England an inch is called inch, its generally accepted sign is quotation marks: for example: 17 ". So a person who decides to buy a TV, for example, should not be embarrassed by a double stroke or the mention in next to the figure characterizing the size of the screen. This is all about the same SI units.
In the United States, as in England, since 1958 an inch is considered equal to 2.54 cm. There this unit is used in various fields, and quite widely - for example, when specifying the caliber of small arms. In America, weapon caliber (barrel bore) is measured in hundredths of an inch. Accordingly, the famous Colt 45 caliber means a weapon with a barrel diameter of 0.45 inches (11.43 mm).
Where is the inch used
A legitimate question arises. Why should a person living in a country where the metric system of measures is used (Russia) be concerned about American length indicators or, say, how to translate mm to inches? But it’s not so simple. Recently, due to the expansion of American technology and the emergence of new technical terms, inches began to be used in Russian much more often. And before, there were entire industries where the mentioned value was considered the main unit of measurement. So, in inches it is customary to measure the caliber of artillery guns. True, this should be dealt with especially. For example, in the UK, unlike the United States, calibres show thousandths of an inch. And the famous Russian “three-ruler” is the 3 mentioned units (7.62 mm).
Inches are also used in the automotive industry: they measure the diameters of the wheels of a car. Since the existence of the Soviet automobile industry began with foreign technologies and licenses, foreign terminology was also used to a large extent. For example, one of the first-born of the domestic automobile industry, KIM-10, had a cylinder diameter of 2 1/2 "(or 63.5 mm). In inches also indicate the diameters of telescope lenses, and they also use this unit to mark pipes.
About trumpet inch
A long tradition is the use of the considered value when working with gas and water pipes, as well as to indicate the threads cut into them. But it should be noted: a pipe inch in mm is not at all the same as a regular inch.
This concept cannot be called scientific, and yet it has a strictly defined meaning. The pipe diameter is considered to be the outer diameter of such a pipe in which the internal diameter corresponds to a normal inch. This value is somewhat arbitrary: the pipes have different thicknesses, which, of course, affects the ratio of diameters. Nevertheless, it was possible to come to some uniformity in this matter.
About conditional pass
Speaking about the parameters of manufactured (rolled) pipes, they usually mean their diameter on the outside. Of course, with the same external values, but with different wall thicknesses, the internal dimensions of different products can vary significantly. Therefore, the concept of the conditional pipe passage was introduced : this is a special internal diameter to which a certain external value can correspond. For example, in a pipe with a passage of 40 mm, the actual internal diameter can be represented by any sufficiently close number.
Why do you need to know this? Then, that the main indicator by which the passage of water is calculated is the inner diameter of the pipe. And in plumbing practice they use steel products, marked in inches, and copper, aluminum, stainless steel, manufactured according to metric standards. Therefore, the correct translation is necessary: inches in mm of the pipe (binding of the considered value to metric values). There are special tables (GOST 3262-75) that establish the correspondence between different types of pipes and their parameters. In them, the value of the conditional diameter (passage) of the pipe is taken as the base.
About threads
Pipes often have to be connected. For diameters greater than 6 inches, welding is usually used, smaller products are twisted with a thread, the parameters of which are usually expressed in inches. Pipe thread pitch is the number of threads placed on one such unit. There are also tables of correspondence of thread steps in mm to the number of threads per inch. There is also a more general table linking the inch dimensions of a cylindrical pipe thread with its metric parameters. In accordance with it, in particular, a thread of 3 inches in mm corresponds to a value of 87.884; 86,405 and 84,926 (nominal indicators of the outer, middle, inner diameters, respectively). In general, pipe threading is a whole science, plus a considerable group of different standards, the goals of which are the correct connection of threaded elements and structures. The basis of these standards are indicators of the inch system of units.
And again about inches
The name “inch” and its derivatives can often be found in the description of other production processes. For example, the word "inch" is sometimes understood as a board with a thickness of an inch or a nail of the same length (in these cases, the translation of inches into mm becomes relevant again). But that is not all. Until now, the concept of "inch" is popular when mentioning fasteners and many other metal products. Nevertheless, this word would be listed in anachronisms, if not for the rapid development of computer technologies, which have brought new terms into our circulation. The resolution of printers and some other devices is usually indicated in dots per inch (dpi). There is the concept of pixels per inch (ppi), used to indicate the resolution of a device that inputs or outputs graphics. The concepts of dpi and ppi are not technologically identical to each other.
In inches, the screens of mobile phones, monitors, diagonal of TVs are also measured (earlier in the USSR this value was expressed in cm). We should talk about screens in a bit more detail.
About pixels and image
Many, talking about television or other screens, consider its size to be the most important indicator. They intensively translate the diagonal length (for example, 21 inches in mm) into more familiar measures for themselves, trying to figure out whether this value is sufficient for them. At the same time, there are indicators not less important, which buyers of such equipment sometimes do not pay attention to.
Pixel is a technical term that has migrated to everyday life. If we move away from complex definitions, then a pixel can be called the smallest indivisible image object of a certain color. A bitmap image of computers is a collection of pixels arranged in rows and columns. The principles of television are somewhat different, but here it’s customary to talk about the resolution of the device, that is, about its ability to display the greatest number of details (units) of the displayed image. Of course, any image is all the more beautiful and high-quality, the higher the number of pixels per unit area of the screen. This is the already mentioned ppi (the number of dots per inch of the display). The ppi value is extremely important for obtaining a bright, clear, high-quality picture, so you should definitely pay attention to it when buying the appropriate equipment.
However, happiness is not only in pixels - at least, as many experts say. The pursuit of high resolution leads to a serious increase in the load on graphics cards. That is, buyers of television and other similar equipment should carefully weigh the pros and cons and stop at the optimal version of the device for themselves.
Inches, inches ...
In computer practice, we recall this value even when we refine the parameters of hard drives, disk drives, and characteristics of a DVD drive. In inches indicate the size of the matrix of digital cameras. What is a matrix and what effect does its size have on image quality? This is a very interesting and important question, but for another discussion.
How to remember the size of an inch?
A person who does not have a good memory for numbers should know the following: 4 inches in mm will be 2.54 * 4, that is, a little more than 1 cm. In cases where special accuracy is not needed, such a scheme can be used in some domestic situations.
Conclusion
If you write the query “inch” in some search engine, then the link to James Aldridge’s short story “The Last Inch” will certainly appear as answer options. This is a small but really worthwhile work that has become a classic of world literature, more than once filmed. A deeply tragic story of human courage, the complex relationship of father and son, the quirks of fate.
But the title of the story is interesting. Why "Last Inch"? In the story, a ten-year-old child, who had never before flown an airplane, had the chance not only to drive a difficult route, but also to land it in difficult and even dangerous conditions. The child did it. The last inch before planting became the frontier, turning him into another person - an adult, responsible, he also highlighted a new facet in the future relations of father and son. So it is not always correct to express an inch in mm - sometimes this value requires completely different approaches and equivalents.