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Text Descriptions for Formulas, Graphs, and Maps |

In some cases it may be appropriate to use text descriptions for formulas, graphs and maps. In order to convey the intended information to users with visual disabilities, the text descriptions must be precise and complete. There are no published rules for writing these descriptions. The National Center for Accessible Media (NCAM) has come up with several guidelines for making educational software accessible. We can apply some of these guidelines to our specific needs. All of the guidelines and checkpoints can be viewed at NCAM's "Accessible Digital Media Design Guidelines for Electronic Publications, Multimedia and the Web." (Graphs are under Guideline F.) Mathematical and scientific formulas have special requirements to accommodate screen-reading software. These are discussed below.

- Math symbols such as = , +, * ,or / should be written out as equals,
plus, times, divided by and so on.
- Abbreviations can be used, but some people might not know the abbreviations,
so we recommend that they be written out. (For example: NC should be North
Carolina; mm should be millimeters.)
- Numbers and integers can be written out in numeric form. (For example:
1, 2, 3, 1.5, 2.5, and so on.)
- Fractions should be written out as well. So 3/4 should be written
as three fourths or 3 over 4, or some combination of the two. 4ths is unacceptable as well.
- If color plays a role in the graph/chart, such as in pie charts,
it is neccessary to establish what each color represents. Also, there are
issues surrounding low vision and color blindness that can arise when using
color coded charts and graphs. See
more on low vision and color blindness.

NCAM Checkpoint F4

Provide a complete description in text for static graphs. Priority 1

In recordings of textbooks on audio tape for use by blind students, narrators routinely describe graphs and charts in words. A carefully scripted description can convey the main points of a graph. This text can be displayed on screen for use by assistive technology, delivered directly by the product with text-to-speech, or delivered programmatically through an accessibility API. See the section on access issues for selected development environments for information on accessibility APIs. The text should describe the layout of the graph, the location of variables on the graph, and the overall trend.

Here is a description example from the National Braille Association Tape Recording Manual (Appendix 4: Guides to Spoken Mathematics):

Figure 5. "The relationship between the vapor pressure of water and its temperature."

This is a line graph whose x-axis is temperature in degrees centigrade, running
from zero to one hundred degrees. The y-axis is pressure in millimeters of mercury
and runs from zero to 800 millimeters. The curve starts at the origin and rises
so that when x is 25 degrees, y is approximately 40 millimeters. When x is 50,
y is 100. When x is 75, y is just under 300. When x is 100, y is about 760.

The next two examples are consecutive slides from a PowerPoint presentation.

This slide is a graph of a Payoff Matrix. A rectangle is the body of the graph
with the values placed on the left side and on top. The 2 variables in this
example are Alternatives and States of Nature. Alternatives subscript i are
listed on the y-axis with 3 different values represented by A subscript 1, A
subscript 2, and A subscript 3, read from the top down consecutively. States
of Nature subscript j are listed on the x-axis with 3 different values represented
by S subscript 1, S subscript 2, S subscript 3, and S subscript 4 read left
to right consecutively.

This slide is the same graph as the previous slide, the Payoff Matrix. There
are values placed in the rectangle for the various corresponding Alternatives
and States of Nature represented by C. The value C is representative of the
consequences between different Alternatives and States of Nature. A subscript
1 and S subscript 1 equal C subscript 11, A subscript 1 and S subscript 2 equal
C subscript 12, A subscript 1 and S subscript 3 equal C subscript 13, A subscript
1 and S subscript 4 equal C subscript 14; A subscript 2 and S subscript 1 equal
C subscript 21, A subscript 2 and S subscript 2 equal C subscript 22, A subscript
2 and S subscript 3 equal C subscript 23, A subscript 2 and S subscript 4 equal
C subscript 24; A subscript 3 and S subscript 1 equal C subscript 31, A subscript
3 and S subscript 2 equal C subscript 32, A subscript 3 and S subscript 3 equal
C subscript 33, A subscript 3 and S subscript 4 equal C subscript 34.

National Center for Accessible Media. "Making Educational Software Accessible: Design Guidelines Including Math & Science Solutions."

Lighthouse International. "Effective Color Contrast: Designing for People with Partial Sight and Color Deficiencies."