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In my high school and college math classes, I've always seen graphs drawn with either no arrows on the ends of the axes or with arrows on both ends.

A colleague recently argued with me that this was crazy and arrows are always placed on one side of each axis to indicate the positive direction. Like so: enter image description here

Which style is more prevalent?

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I think the convention of having the positive directions be right and up are pretty well set, making the arrows pretty unnecessary for anything besides decoration. – RHP Jul 19 '11 at 22:28
I don't put arrowheads, but if I saw them then I would prefer them positive only. Note that on a map, there is often only one, for North. – Henry Jul 19 '11 at 23:23
I have to say that as a mathematician I am continually surprised at the number of questions on this site which are purely about conventions of various kinds (notation, terminology, practices). If it makes anyone feel any better: I give you permission to draw your axes however you want! (Does it make anyone feel any better?) – Pete L. Clark Jul 19 '11 at 23:31
@Pete I agree completely; when it's a question of "what should I write for this assignment?", it does not matter at all (and if it does, then the teacher/professor probably already specified). When it's a question of "what should I write in this paper?", again it shouldn't matter as long as whatever you use is clear. However, I'm working on the exercise framework for Khan Academy, a situation where it is important to use whatever convention will be the most comfortable for students. – rubergly Jul 19 '11 at 23:43
@rubergly: What you say in your last comment sounds like better motivation than winning a rather pointless argument with your colleague. Perhaps you should edit that into your question. (Still, it's not clear to me that there will be a definitive answer to questions like this.) You might just want to flip through a stack of math textbooks at approximately the same grade level as your course and see if there's any unanimity to what they do. – Pete L. Clark Jul 19 '11 at 23:50

I've always assumed arrows indicate the positive direction.

Wikipedia is not as reliable in these really elementary articles than in more advanced ones, just because all of the millions of people who see such topics in school want to contribute and experts may find it boring to look at kindergarten-level stuff. Wikipedia should not be considered authoritative, even though it's often an excellent starting point.

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I guess I could have been clearer, but when I said "Which style is more prevalent?" I meant among textbooks and classrooms for kids learning basic math. – rubergly Jul 20 '11 at 5:39

In my engineering classes, when there are many axes, (for the multiple coordinate systems) the arrow always points in the positive direction for that axis. It would not be easy to indicate which direction was positive without this standard. So while it may be unnecessary for elementary graphs, being consistent helps students learning. So regardless of which style is more prevalent at a particular grade level, to be consistent with advanced coordinate systems, the style where the arrow indicates the positive direction should be used.

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