A question we frequently encounter in display design involves the sizing of objects on a process display. Most people asking this question are expecting a simple answer, such as, “Use a 12 point font for text.” Unfortunately, the answer is much more complicated. Multiple variables impact the sizing of objects on process displays, including screen size, resolution, and viewing distance.
Space on a computer monitor is divided into pixels. The number of pixels on the monitor is determined by its resolution, which is variable. Standard resolutions include 1600x1200, 1280x1024, etc. The actual size of each pixel depends both on the resolution and the monitor size. A higher resolution results in more pixels per inch, which makes the same size (in inches) shape on the same monitor appear smaller at a higher resolution. This concept is easy enough to demonstrate by adjusting the resolution on your computer monitor. As you increase the resolution, everything appears smaller in size.
The following table further illustrates this concept by showing the number of pixels per vertical inch for a 20-inch monitor at two different resolutions. This has implications when designing shapes for use on a graphical process display.
Specifying object height in pixels could result in the two different analog bars shown. Both bars are 60 pixels in height, but appear different due to the difference in resolutions. How then, should shape size be specified? From a human factors perspective, visual angle, or the angle formed by two straight lines drawn from the extreme points of an object to the center of the eye, needs to be calculated to ensure that minimum standards are met. According to ANSI standards, the minimum visual angle should be between 10 and 16 minutes of arc, depending on how the information is to be used.
Beville’s website includes a new shape sizing feature to help you determine the height required for your graphical shapes. Once you provide the viewing distance and select a visual angle from the guidelines, suggested height in inches will be provided. If resolution and monitor height are also provided, required height in pixels will also be given.
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