Science Chats Forum

When I was in elementary school, there was one teacher who would always write the number 7 with a line through the middle, and I never knew why. I just assumed it was a personal preference and I started doing it for awhile myself.



Well, I stumbled upon this slide show on the Arabic numbers that gives an explanation on why all of our numbers (1 - 9, and 0) are shaped the way they are and that also answers my question on the number 7.

http://www.slideshare.net/nzar/numbers-1218076

Attached Images

7.png (645 Bytes, 13 views)

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You open my curiosity on the subject, now I want to know the detailed explanation on the line, what is it? Isn't it just to distinguish it from 1?

The slideshow Carrera linked to explains it better, but basically the video shows that each numeral graphically represented the value it stood for in the number of angles present in the figure. For instance, the character for 1 contained one angle, the character for 7 with the stroke contains 7. Somewhere along the line we lost the stroke, but it is alive and well in many cultures. I believe the French still add the stroke to their 7s.

The line through the 7 is, indeed, there to distinguish it from the European 1, which has a pronounced leading line (much larger than the 1 in this type font). Why the line? Easy. The numbers are not written relative to the writing line the same as in America. The circle of the nine, for instance, rests on the writing line with the tail dangling (like a "g"). There's no need for a line on it because it's unambiguous. The 7 likewise breaks the line.