Do you remember the little girl from the fairy tale, Thumbelina? Ever thought about the origin of her name? Let's talk about it.
About the word "inch"
In Dutch, the word "inch" means "thumb". This is a measure of length equal to the width of the thumb of an average person (although some people claim that we are talking about the length of his upper phalanx). But, no matter what part we are talking about, it turns out that Thumbelina is a girl the size of a finger.
By the way, another hero of the same size is known in the fairy tale epic. It turns out that our beloved Thumb-Boy could also be called Thumbelina by analogy. Joke, of course. However, people's fingers are different, so I would still like to clarify: how many mm are in an inch?
About the size of an inch
Determining what an inch is in mm is not so easy. 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 Viennese inch was equal to 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 hardly be replenishedor not to infinity. Each of the German lands had its own type of the mentioned measure of length, different from the others: 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 territories of the Commonwe alth, there were Old Polish and New Poland 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 cun (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 equates to 16.93mm.
About the Metric Convention and the Metric System of Measures
May 20, 1875 in Paris, in the building of the Ministry of Foreign Affairs of France, the so-called. The metric convention is an agreement designed to ensure the uniformity of international metrological standards. Russia also joined this agreement - on behalf of the emperor, the agreement was signed by Okunev, an adviser to the embassy. The adoption of the convention served as an important impetus in the development of the metric system of measures and the beginning of the development of standards for the meter and kilogram. Later, the basic units of quantities were introduced in the fields of electricity and optics. More than 50 states, including all the most industrialized ones, are currently affiliated 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, OIML (International Organization of Legal Metrology)strongly recommends that it be withdrawn from circulation as soon as possible where it is still used for measurements (the reason, I think, is clear). Second remark. The largest and highly developed country of the United States, although it signed the Metric Convention, still does not consider it obligatory to use the metric system of measures. The inch is widely used as a local unit of measurement, which makes it very difficult for the rest of the world to follow the recommendations of the OIML.
About the English inch
So what is this unit anyway, how to express 1 inch in mm? At present, when this term is mentioned, as a rule, it refers to the English, or imperial measure of length. Its value has also changed several times, but since 1958, converting inches to mm will give a result of 25.4 per unit. So the dimensions 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 recognized sign is quotation marks: for example: 17 .. It's all about the same SI units.
In the US, 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 indicating the caliber of small arms. In America, gun caliber (barrel bore diameter) is measured in hundredths of an inch. Accordingly, the famous Colt 45 means a weapon with a barrel diameter of 0.45 inches.(11.43mm).
Where inch is used
A legitimate question arises. Why should a person living in a country where the metric system of measures is used (Russia) care about American length indicators or, for example, how to convert mm to inches? But everything is not so simple. Recently, due to the expansion of American technology and the emergence of new technical terms, inches have become used in Russian much more often. And even 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 calibers of artillery pieces. True, this should be de alt with separately. For example, in the UK, unlike the US, calibers 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 to measure the diameter of a car's rims. 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 automotive industry, KIM-10, had a cylinder diameter of 2 1/2 (or 63.5 mm). In inches, the diameters of telescope lenses are also indicated, and this unit is also used to mark pipes.
About pipe inch
It is a long tradition to use the quantity in question when working with gas and water pipes, as well as to indicate the threads cut into them. Butnote: pipe inch in mm is not the same as regular inch.
This concept can not be called scientific, and yet it has a strictly defined meaning. Pipe inch is considered to be the outer diameter of such a pipe, in which the inner diameter corresponds to the usual inch. This value is somewhat arbitrary: the pipes have different thicknesses, which, of course, affects the ratio of diameters. And yet, 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 outside diameter. Of course, with the same external values, but with different wall thicknesses, the internal dimensions of different products can differ significantly. Therefore, the concept of nominal pipe diameter has been introduced: this is a special internal diameter, which can correspond to a certain external value. For example, in a pipe with a passage of 40 mm, the actual inside diameter can be represented by any sufficiently close number.
Why do you need to know? Then, that the main indicator by which the passage of water is calculated is the inner diameter of the pipe. And in plumbing practice, both steel products, marked in inches, and copper, aluminum, stainless steel, produced according to metric standards, are used. Therefore, a correct translation is necessary: inches to mm of pipe (binding the value in question to metric values). There are special tables (GOST 3262-75) that establish a correspondence betweendifferent types of pipes and their parameters. In them, the value of the conditional diameter (passage) of the pipe is taken as the base one.
About threads
Pipes often have to be connected. For diameters over 6 inches, welding is usually used, smaller products are twisted using threads, the parameters of which are usually expressed in inches. The pitch of a pipe thread is the number of threads placed on one such unit. There are also tables of correspondence of thread pitches in mm to the number of threads per inch. There is also a more general table that links 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 the values 87, 884; 86, 405 and 84, 926 (nominal values of external, average, internal diameters respectively). In general, pipe thread is a whole science plus a considerable group of different standards, the goals of which are the correct connection of elements and structures with a thread. These standards are based on the inch system of units.
Inches again
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 an inch thick or a nail of the same length (in these cases, the conversion of inches to mm again becomes relevant). But that's not all. Until now, the concept of "inch" is popular when referring to fasteners and many other hardware. And yet this word would be listed in anachronisms, if not for the rapid developmentcomputer technologies that brought new terms into our circulation. The resolution of printers and some other devices is usually specified in dots per inch (dpi). There is also the concept of pixels per inch (ppi), used when specifying the resolution of a device that inputs or outputs graphics. The concepts of dpi and ppi are technologically not identical to each other.
Screens of mobile phones, monitors, TV diagonals are also measured in inches (earlier in the USSR this value was expressed in cm). It is worth talking about screens in a little more detail.
About pixels and image
Many, talking about television or other screens, consider the most important indicator of its size. They intensively convert the length of the diagonal into more familiar measures (for example, 21 inches in mm), trying to figure out whether this value is sufficient for them. At the same time, there are indicators no less important, which buyers of such equipment sometimes do not pay attention to.
Pixel is a technical term that has migrated into everyday life. If we move away from complex definitions, then a pixel can be called the smallest indivisible object of an image of a certain color. A computer bitmap is a collection of pixels arranged in rows and columns. The principles of television are somewhat different, but even here it is customary to talk about the resolution of the device, i.e., its ability to display the greatest number of details (units) of the displayed picture. Of course, any image is more beautiful and high quality, the higherthe number of pixels per unit area of the screen. This is the already mentioned ppi indicator (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, many experts say so. 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 all the pros and cons and stop at the optimal device option for themselves.
Inches, inches…
In computer practice, we remember this value even when we specify the parameters of hard drives, disk drives, DVD drive characteristics. In inches indicate the size of the matrix of digital cameras. What is a matrix and what impact 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 2.544, i.e. a little more than 1 cm. In cases where special accuracy is not needed, such a scheme it is quite possible to use in some everyday situations.
Conclusion
If you write the query "inch" in some search engine, then a link to the story will certainly appear as answer optionsJames Aldridge "The Last Inch". This is a small but really worthwhile work, which has become a classic of world literature, filmed more than once. A deeply tragic story of human courage, complex relationships between father and son, whims of fate.
But the title of the story is interesting. Why "The Last Inch"? According to the plot, a ten-year-old child, who had never flown an airplane before, had a chance not only to drive a car on the most difficult route, but also to land it in difficult and even dangerous conditions. The child did well. The last inch before landing became a boundary that turned him into another person - an adult, responsible, he also highlighted a new facet in the future relationship between father and son. So it is not always correct to express an inch in mm - sometimes this value requires completely different approaches and equivalents.
