Dynamic Displays

Introduction
a. Definition - Displays which present information which continually changes with regard to condition. Examples are gauges, radar, etc.
b. Types -
(1) Quantitative Displays - present numerical information in digital ("counters", numerical indicators) or analog (scale and pointer) format.
(2) Qualitative Displays - status indicators giving an approximate value or trend or rate of change (e.g. on/off, open/closed, full/empty).
(3) Representational Displays - maps (e.g. airplane radar, computer interface).

Quantitative Displays
a. Digital Displays
(1) Preferred - when precise numeric values are required, legible digits are needed quickly or the value remains stable for a long enough period to be read.
(2) Design Rule - use a dark background and light numbers.

b. Analog Displays
(1) Preferred - when direction of change is important, rate of change is important, or anticipatory information is important.
(2) General Design Rules -
(a) Moving pointer on a fixed scale is preferred.
(b) If numerical change relates to natural function (e.g. up/down) then vertical display is preferred to circular display.
(c) Don't mix types of pointer-scales to indicate related functions in displays.
(d) Direction of movement of pointer should match that of the control.
(e) If value must be read quickly then a moving scale appearing in an open-window is best.
(f) Where possible use semi-circular or circular displays rather than horizontal or vertical displays.
(g) Adjacent scales should have similar markings and be oriented to the same point to indicate normal operation. This is exemplified with check scales.
(h) Use dials with target zones where possible because these are faster and easier to read. Mark zones with labels and colors. For aircraft define where they should be. For autos define where they shouldn't be.

(3) Specific Design Rules (see course text book,  fig 5-6 p. 140)
(a) Numerical Progression -
(i) intervals of 1 are easiest to read (0, 1, 2, ...)
(ii) decimal progression is the second most preferred (10, 20, 30, ...)
(iii) units of 5 is the next best (5, 10, 15, ...)
(iv) intervals of 2 are also OK (2, 4, 6, ...)
(v) avoid unusual progressions (e.g. by 3, by 7, by 8)
(vi) scale intervals should represent consistent progressions (all intervals should equal the same amount)

(b) Scale Markings -
(i) length depends on level of illumination - markers must be thicker and farther apart in low light
(ii) markings should be presented for the smallest scale unit that needs to be read
(iii) use different interval markers (in gradations like a ruler)
(iv) zero should be placed at 6 o'clock or 12 o'clock (standard for auto industry is 7 o'clock however)

(c) Scale Type -
(i) type should be upright and from left to right not slanted at an angle radially
(ii) use simple fonts and legible printing

(d) Scale Markers and Interpolation - is the estimation of value being displayed. To maximize accuracy:
(i) use a linear scale
(ii) interpolations should be in decimal scales - 5's or 10's
(iii) fastest when pointer is on a marker

(d) Pointers -
(i) use a tip angle of 20%
(ii) tip should touch smallest scale markings but not obscure them
(iii) to avoid parallax, pointer should be as close to the scale surface as possible (may have to raise scale markings)
(iv) clockwise motion is preferred to indicate increase

(e) Illumination -
(i) maximize contrast
(ii) in low illumination use white pointer and markings on a dark background
(iii) reverse for high illumination

(f) Scale Size and Viewing Distance -
(i) to find necessary size of dimension multiply dimension standard (at 28") by its viewing distance in inches and divide by 28, i.e. Dimension at viewing distance (X) = Dimension at 28" (d28) x X/28. (where all dimensions are in inches)

Check Displays
Refers to reading a display to check that all is well. In check reading the `normal' position should be either at 9 or 12 o'clock and all pointers should be aligned similarly. The addition of a line between the dials can increase the strength of the `gestalt' for the display.

Electronic Quantitative Displays
With non-numeric bar-type displays these are best read when only one segment is indicated. Although with a variable such as speed where rate is important, a complete bar-type display that grows longer or shorter may be more relevant.

Qualitative Displays
a. Example - The center-mounted brake light is a US compulsory standard because of ergonomic research. Of the 25% of all traffic accidents involved rear end collisions, 7.4% of these were fatalities. People used the distance between brake lights to gauge distance of car ahead of them. In 1977 researchers looked at 2100 taxis. A 54% reduction in rear-end collisions was found with a high rear-end brake light.
It was estimated that it would prevent ~ 1.7 million accidents and ~ $1 billion in repair costs alone. In 1980 Bell Telephone's 5400 company vehicles had CMHBL (center mounted high brake light) and had a 53% reduction in collisions.

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