# Line-numbers or chalk-board to Math SE?

I would like to point out certain locations specifically by line numbers or by some marking, how can I do it in long answers such as here? It would help communication enormously.

Chalks, where are they?

• The LaTeX supported by MathJax has options for numbering equations. – Dylan Moreland Feb 20 '12 at 1:01
• You can use \tag{1}, for example, after an equation to label that line as equation 1. For an example, see here. – JavaMan Feb 20 '12 at 2:05
• At first I couldn't understand why you said, "Sorry [for the] stupid and arrogant suggestion", because the first paragraph seemed like a perfectly reasonable request about a issue relevant to everybody. Then I read the rest of the paragraphs... – Rahul Feb 20 '12 at 5:53
• You say below "you may be fed up reading the dxmp initial stream of consciousness -- I brainstormed by purpose to get ideas, cannot see nothing wrong in it." I find this attitude to communication extremely presumptuous and not very good manners. Innit? – user16299 Feb 22 '12 at 2:02
• Regarding the addition of the "pony" tag, I can only direct the OP to the 6th entry here en.wiktionary.org/wiki/pony – user16299 Feb 26 '12 at 23:01
• @Yemon: While I certainly agree with your disdain for the original version of the question, it's now been heavily edited. Also, the all-caps is a bit much; if you must emphasize, you can use *text*, **text**, or ***text*** for italics, bold, or both. I'd ask that you delete your most recent comment. – Zev Chonoles Feb 28 '12 at 23:34
• @ZevChonoles, my request was in direct response to the author adding facetious tags like "pony" and bumping the question without, in my view, making the question better. The attitude evinced here and on another question is what led me, while fully aware of the online meaning of all caps, to use it nonetheless. That said, I shall delete the comment as you request. – user16299 Mar 1 '12 at 0:32
• @Rahul. As perhaps one of only two people on this site who actually like the (pony) tag, I was tempted to be upset that you edited it out, until I realized that since there was such an easy solution to hhh's problem the tag was indeed inappropriate in this case. – Rick Decker Oct 6 '12 at 1:44

A magical real-time multi-user gestural touchscreen whiteboard interface would be pretty awesome, but let's face it, we're talking about StackExchange here, and not, say, Industrial Light & Magic. You might as well ask for a pony while you're at it.

Equation numbers can be added by including \tag{n} at the end of the equation, as JavaMan said in a comment. If you need to refer to equations in someone else's answer that don't have numbers, you can do two things:

1. Earn 2000 reputation points as fast as possible. Then edit their answer to include equation numbers, and refer to the numbers.

2. Post a comment saying, "Your post has a lot of equations and I need to refer to a specific one. Can you add numbers using the \tag{n} command?" Hopefully, the author or someone else with 2000 rep will come along soon enough and edit those in.

• A real-time multi-user gestural touchscreen whiteboard interface would be mediocre, but I agree that a magical one would be awesome. – Tsuyoshi Ito Feb 20 '12 at 19:23
• That is because you do not know that it is possible to do. I think it was Django -book that had some way of adding marks etc on the online book -- something like that made look like chalks would work here -- or easier edit, nothing pony here. Perhaps, you got fed up reading the dxmp initial stream of consciousness -- I brainstormed by purpose to get ideas, cannot see nothing wrong in it. But yes "A magical real-time multi-user gestural touchscreen whiteboard interface" would be awesome -- that is a challange for OCR and FPGA developers among quants/etc --What a PONY challenge, let's do it :P – hhh Feb 21 '12 at 0:17
• Why ask for ponies when you can have unicorns? – Tobias Kienzler Mar 14 '12 at 12:34

I know one way of doing this: building iPad -site or iPad -app for Math SE but currently not feasible because of the restricted API. This so-called site could act like a virtual chalkboard -- it could be super-cool.

Initially, I probably thought this problem the wrong/hard way i.e. through OCR such as here, here and here -- but in reality, you can get this problem into much simpler form if you develop the site on something with touchscreen, otherwise I cannot see how to do it easily. With specified framework, it should be easier -- I may be of course mistaken.

There may be other solutions.

Perhaps related

1. Tablet for reading textbooks and writing math by hand? and particularly my answer here

2. A digital notebook for Mathematics? and my answer here