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Math Equations & Formulas

Fri, 03/27/2009 - 17:18 — kvl5046

This Page

  1. Synopsis
  2. Equations as Text
  3. Unicode Support for Math Symbols
  4. JAWS Symbol File
  5. Using an Image
  6. Math ML
  7. Links on Math and Accessibility

Synopsis

  1. Provide a label for each formula or equation whether the equation is an image or text.

  2. Whenever input math equations as text, especially if they are one one line. The visuals will be generally be of higher quality, especially for low vision users. Symbols should be inputted in Unicode encoding whenever possible.

  3. If a screen reader cannot interpret a symbol, then you may be able to append a pronunciation file (particularly in Jaws 6.1 +).

  4. If a pronunciation file cannot be appended, then use hidden text (e.g. ALT text of an invisible graphic) to spell out the formula replacing symbols like ≠ with words like "not equals".

  5. Provide ALT tag for any images used spelling out the formula. If the description is over 255 chracters, then link to an extended text description

  6. PDF files or Word Files can be beneficial, but make sure the content is accessible to screen readers.

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Equations as Text

As mentioned in the recommendations for Images, complex images may require a link to a longer text description depending on how critical it is to the content. Here is a line chart for tracking preferred computer platform over time.

Inaccessible Snell's Equations

In HTML (Extended Text Description Below)

ni sinθi = nr sinθrN sub I times sine theta sub I = N sub R times sine theta sub R

View the Code

n <sub>i</sub> sin <font face="Symbol">q</font>i = n <sub>r </sub> sin&theta; <sub>r</sub>

This code includes the SUB subscript tag, changes the font to "Symbol" for one theta and uses the &theta; entity code (better) for the other instance.

What the Screen Reader Says

Knee sinqui equals ennar sin question-mark R.

The "question-mark" indicates the screen reader was not able to decipher the &theta; entity code.

 

Adding a Label and Text

Snell's Equation- ni sinθi = nr sinθrN sub I times sine theta sub I = N sub R times sine theta sub R

Extended Description - N sub I times sine theta sub I equals N sub R times sine theta sub R.

The label "Snell's Equation" gives a user of a screen reader an idea of the content is and an extended text description gives the full details. An extended description can be linked or incorporated into the text as needed.

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Unicode Support for Foreign Language

In most cases, non-English text (including special characters such as ©, †) should be inserted as is into a document encoded in Unicode. The Penn State Computing with Accents and Symbols page has information about math symbol codes for HTML

Note on Word

Unfortunately the Insert Symbol tool in Word 2003 (Win)/2008 (Mac) does not insert the correct Unicode value for a math symbol. If the text is migrating to a Web platform or a user reports problems, then use the Windows Character Map or the Mac Character Palette to insert the symbols. Windows users should switch to the Arial Unicode MS font.

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JAWS Symbol File

If JAWS is unable to recognize a particular symbol in a document, you can append a Symbol File (.sbl) file which assigns plain text values to a Unicode character. For example the cube root symbol ∛ (Unicode character code number U+221B) can be set as "U+221B = cube root"

Links to information and text files for math and phonetics are at Getting JAWS 6.1 to recognize "exotic" Unicode symbols

Note: This applies to JAWS 6.1 and later.

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Using an Image

When an image is used, there should be a label for each equation and the ALT tag should specify how to read the symbols. The safest option is to spell out the symbols as words (e.g. ± as " plus or minus "). If the ALT tag is over 255 characters, then you can link to an extended text description.

Go to the example below for an accessible use of an image to represent a formula.

Accessible Use of Image for an Equation

Quadratic Formula

X equals negative b, plus or minus the square root of B squared minus four times A times C all divided by two times A

View the Code

<img src=quatratic.gif alt ="X equals negative b, plus or minus the square root of B squared minus four times A times C all divided by two times A">

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Links on Foreign Language Accessibility

These links are primarily about accessbility policy in other countries, but there may be technical information provided. Organizations supporting visually impaired persons may also be another path to explore.

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Math ML

Math ML is an XML platform designed to deliver equations as text. Equation Editors such as MathType can convert equations to MathML, however there are some issues to consider.

Unfortunately, as of April 2008, there are two incompatible MathML flavors in use – one for Internet Explorer and the official W3C MathML version used by Firefox and Opera. There is no simple way to used the same code on all three browsers. A common solution is to use scripting to present one of two versions based on the user's browser... or to avoid MathML for now.

Jaws can recognize the Internet Explorer version of the MathML if the MathPlayer plugin is installed (but no Mac viewer could properly view that page). If a user needs MathML, a page with equations in one of the two flavors a page listing the equations can be developed if an editor which can export MathML is used.

If browsers evolve to use just one version of MathML, developers may be able to replace images with MathML in a future revision.

Links on Math and Accessibility

General Math Accessibility

Unicode and MathML

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