Question 2 of 7: Displays, Control Design, and Workplace Layout Priorities

Question 2: Displays, Control Design, and Workplace Layout Priorities (20 marks: i–7, ii–7, iii–6)

Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.

(i) Basic and Specific Features of Quantitative Displays

A conventional quantitative display (dial, gauge, digital counter) exists to let an operator read a numeric value quickly and accurately. Its basic features are the ones common to any display: adequate size and contrast for the expected viewing distance and lighting, a scale range that covers all values the process can produce without the pointer running off-scale, and legible, evenly-spaced graduation marks and numerals oriented for easy reading. Its specific features concern how the numeric value is actually read: the choice between a moving pointer/fixed scale, a moving scale/fixed pointer, or a digital (counter) display trades off ease of seeing the direction/rate of change (best with a moving pointer) against reading-precision and speed for an exact value (best with a digital counter); scale-interval choice (progression by 1s, 5s, or 10s reads fastest — irregular intervals such as 3s or 7s slow reading and increase error); and the presence of check-reading aids such as a coloured band marking a normal operating zone, which lets an operator confirm "all is well" with a glance rather than reading the exact number.

(ii) Factors to Consider in Control Design

Control design must jointly satisfy the task, the operator population, and the environment. Key factors are: the type of control action required (discrete on/off/select vs. continuous quantity setting) dictates whether a switch/pushbutton or a continuous knob/lever/slider is appropriate; size, shape, and resistance must fit the anthropometric range (5th- to 95th-percentile hand/foot dimensions and strength) of the intended user population, including any expected gloves or protective equipment; direction-of-movement compatibility with population stereotypes and with the display it operates (e.g., clockwise rotation should increase the displayed value); the control-response ratio appropriate to whether the task needs speed (low C/R) or precision (high C/R); adequate spacing and grouping to prevent accidental activation of an adjacent control, especially for safety-critical controls; and coding (shape/size/colour/location/label, per Q1(ii)) so the correct control is identified quickly and, ideally, without looking.

(iii) General Guidelines for Displays-and-Controls Workplace Layout

Sanders & McCormick give the general guidelines for a workplace that involves visual displays and controls as an explicit priority sequence: (1) primary visual tasks are given the best viewing positions (near the normal line of sight, at a suitable viewing distance); (2) primary controls that interact with those primary visual tasks are placed next, within easy reach and close to the displays they affect; (3) control-display relationships — each control is located near, and moves compatibly with, its associated display (population stereotypes); (4) elements used in sequence are arranged in that operating sequence; (5) frequently used elements are put in the most convenient locations; and (6) the layout is kept consistent with other layouts within the same system and with similar systems the operator also uses, so learned habits transfer and are not violated. These priorities apply the general component-arrangement principles of Q7(i) — importance, frequency of use, functional grouping and sequence of use — with importance normally prevailing over frequency where the two conflict (a critical but rarely used item still gets a prominent, accessible place).