Human Factors Criteria for the Design and Acquisition of ... - FAA

Keyboards June 20049.9 Key labeling• 9.9.1 Easily legible. Keyboards shall be free fromreflection and have easily legible characters under thelighting conditions of the intended operationalenvironment. [Source: Ilg, 1987; NUREG 0700, 2002]9.9.2 Font for keyboard labels. Keyboard labels should bein a sans serif font. [Source: Nolan, 1991]9.9.3 Single letter font. Single letters on keyboard keysshould be upper case. [Source: Nolan, 1991]• 9.9.4 Durability of key labels. The labels on the keys shallbe durable enough to withstand normal wear and tear(including routine cleaning) for the life of the keyboard.[Source: NUREG 0700; 2002]• 9.9.5 Contrast of labels. Key labels may be darker orlighter than the background but shall maintain a luminancecontrast ratio of at minimum 3:1 or a contrast modulationof 0.5. [Source: ANSI, 1988; NUREG 0700, 2002]Additional information. In general, higher luminancecontrasts support better legibility, which can improveperformance. The recommendations above are minimums,applicable to tasks with no time constraint and low risks.Tasks that require rapid and accurate perception of thesymbols may require much higher contrast ratios. Acorrection formula requiring higher luminance contrastsmust be applied to characters smaller than 20 min of arc tooffset the effects of blur in the eye’s optics.In most situations, (based on research done on printed text)black letters on a light background will be more legiblethan white letters on a black background. Research hasfound that white isolated capital letters on a blackbackground are 23.6 % less legible than black on white.[Source: Tinker, 1963, 1965]9.9.6 Primary symbol height. The size of the primarysymbols on the keys should be a minimum of 2.5 mm (.1in) in height. [Source: Grandjean, 1969; NUREG 0700, 2002]9-26