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I'm on a plane and noticed the use of all caps on the flight crew phone:

enter image description here

Generally I found the phone very well designed: it has rounded colors, decent contrast, is unobtrusive for passengers, and has sensible labeling that sections content into islands and even provides nice grid alignment for the text. There are also leader lines to relate the text to the phone numbers. And the work flow is clear from top to bottom ("Lift handset" plus the arrow).

For such a thoughtful design, the one thing that stood out was the use of ALL CAPS in the labels. This makes them less readable I think.

Question:

Is there a good reason or reasons why all caps would be more usable to flight crew in this situation than title or paragraph case?

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Vartabedian, A. G., published in 1971 that people can recognize isolated words better if all capital letters are used. “The Effects of Letter Size, Case, and Generation Method on CRT Display Search Time.” Human Factors, 14, 511-519, in Wickens.

Abstract:

The effects of letter size, case, and generation method were studied in a task of searching for a common five-letter word in a CRT display. Symbol sizes of 0.12, 0.14, and 0.16 in. were evaluated. Words were composed of all uppercase or all lowercase letters. Two symbol generation methods-letters drawn by means of continuous strokes and by means of a seven-wide-by-nine-high pattern of dots in a fixed matrix-were investigated. The results indicated that for both methods of symbol generation, uppercase words were searched 13% faster than lowercase words. No significant differences were found due to symbol generation method or letter size.

Alex Feinman, in the comments below, points to a more recent by Aries Arditi and Jianna Cho published in 2007, Letter case and text legibility in normal and low vision

Abstract:

It is thought by cognitive scientists and typographers alike, that lower-case text is more legible than upper-case. Yet lower-case letters are, on average, smaller in height and width than upper-case characters, which suggests an upper-case advantage. Using a single unaltered font and all upper-, all lower-, and mixed-case text, we assessed size thresholds for words and random strings, and reading speeds for text with normal and visually impaired participants. Lower-case thresholds were roughly 0.1 log unit higher than upper-. Reading speeds were higher for upper- than for mixed-case text at sizes twice acuity size; at larger sizes, the upper-case advantage disappeared. Results suggest that upper-case is more legible than the other case styles, especially for visually-impaired readers, because smaller letter sizes can be used than with the other case styles, with no diminution of legibility.

This notion is brought forward into the U.S. Military Standard 1472, which guides the Human Engineering for all military systems including aviation. The appropriate requirement we must meet for labeling is as follows:

5.2.2.4.4 Labels. To make the display as meaningful as possible and to reduce user memory requirements, every field or column heading shall be labeled. Labels shall be unambiguously related to the group, field, or message they describe. Labels shall be highlighted or otherwise accentuated to facilitate user scanning and recognition. Labels shall be unique and meaningful to distinguish them from data, error messages, or other alphanumerics. Labels shorter than three words shall be displayed in upper case only. Labels longer than three words shall be displayed in upper and lower case.

While not part of the DOD, both the FAA and airplane manufactures borrow heavily from these standards. This is done for multiple reasons including safety (i.e., the reason why the MIL-STD says you should do it) and also cost -- in the case of airplane manufacturers you only have to design it once.

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    And here's a more recent cite: ncbi.nlm.nih.gov/pmc/articles/PMC2016788 Ironically we are often taught that lower case is more readable, owing to an even earlier study. – Alex Feinman Jun 8 '15 at 20:12
  • @AlexFeinman, great cite - thank you! I added a link and quoted the abstract back up into the main answer. I especially like this version, because I can get the full text online! :) – Evil Closet Monkey Jun 8 '15 at 20:17
  • Universal Principles of Design states: "People recognize words by letter groups and shapes. Uppercase text is more difficult to read than sentence case and title case because the shapes of uppercase words are all rectangular." I suspect this is correct in some situations (long text for non-impaired)? – Izhaki Jun 8 '15 at 20:49
  • @Izhaki - mixed case does tend to have a higher rate of recognition for sentence length strings. I'll try and dig up some items on that... but honestly, just go online and try to read someone "YELLING" for full paragraph. :) But for short blocks (e.g., see MIL-STD-1472's requirement of 3 words or less) of text, all upper case can improve reading speed or at least not hinder it. – Evil Closet Monkey Jun 8 '15 at 20:57
  • @EvilClosetMonkey - that's exactly what I was implying. The answer could give one the impression that all caps are always better. – Izhaki Jun 8 '15 at 21:22
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Design of anything in an aircraft is heavily regulated. It is likely there is a viewing distance requirement for the text and that it would be translated into an appropriate character height. If you go to mixed case, the height of the smallest lowercase letter would need to be the appropriate character height. This would roughly double the font height of the text required to meet the requirement.

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For me it seems that the available space is quite small, colors are not optimal for normal reading conditions (gray text -or "dirty white" maybe due to low light or dust- on black background) and lines have just 1 to 3 words.

Taking that into account the main goal would be just to get sure the text is readable (just effectively, since the text is very short efficiency is not needed) and to know it, this should be user-tested. Although lowercase has been proven several times to be easier and faster to read, I don't see that playing a huge role here. If I'd have to guess in this small-available-space context, I'd have several reasons to go with the Uppercase:

  • Letter-size and Readability relationship: The first letter is usually capitalized (uppercase) so using lowercase will inevitably result into a smaller final size of the letters, making then even smaller than the uppercase ones, that are already small, thus reducing readability.
  • Space required and simplicity: In relation with the previous point, using lowercase will also bring some troubles with descenders (ascenders too, but not that much). The simple line separators presented in the design would need to be redesigned or removed to avoid and then you'll need space for the whole font height (and not just the uppercase height, that is shorter)

enter image description here

  • The width of uppercase letters tends to be the same or larger than the same letters in lowercase, which offers a little increase in contrast, which may help in this case.

enter image description here

  • How can a pixel width have an impact on contrast so much? I am trying to understand if its function of font style/selection or there is any supporting fact? – pzv Jun 8 '15 at 4:31
  • I doesn't make a big difference by itself, but in this case where you can see that the font size is small and the contrast is not great ( due to lack of light or dust maybe, but the text seems more gray than white) anything that improves it is preferable. – Alejandro Veltri Jun 8 '15 at 4:53
  • @pzv, don't think of it as one pixel, think of it as 25% of the width of that lower-case l. Then it's clearer how it can make a big difference... – Alex Feinman Jun 8 '15 at 20:30
  • @rewobs agreed! – pzv Jun 9 '15 at 4:17
  • @AlexFeinman I see the point now! – pzv Jun 9 '15 at 4:17
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The only idea that comes to mind is that it might make the phone a little less friendly to the general public. Making it appear too welcoming may invite those who are not flight crew to try and use it.

I'm not saying it's a good idea -- there are better ways to make the device's use appear restricted without impeding its usability. It's just the only explanation I can think of.

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Its all about readability in the given space.

Given the space to contain all the information is anyways quite low. And using lowercase may become difficult to read.

And then , wear and tear of the surface due to handling the phone(over a period of time). As the surface smooths out, lowercase letters will be first to get eroded/faded, making them difficult to read.

But after a quick visualization, readability can be judged from a sample view shown below. Only issue i see is the descender in lowercase strokes, for example "y", will require more spacing between lines.

enter image description here

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