When selecting using a slider, it is easy to reach the positions at the ends of the scale, and it is more difficult to stop in other positions, in between. A typical selection fault is of missing a position in the middle of the scale.
This kind of hazards is typical of operating under stress, when the attention is focused on other tasks (typically, a primary, critical task). Often, it is attributed to careless operation.
If the selection is of a member from an ordinal set, the positions should correspond to that order. For example, a selector of operation speed may be such that the lowest speed is selected using the position on one end and the highest speed is selected using the position on the other hand.
It is best to locate the slider vertically, and assign the highest value to the top and the lowest value to the bottom of the slider.
In the selection is from a set of various, unrelated meanings, the options may be classified according to a forecast of the frequency of using them.
For example, if the On-Off switch of a radio receiver is extended to also include an alarm mode, the alarm mode should be assigned to the position between the On and Off positions, to avoid unintentional setting (see the Clock of Cinderella).
Updated on 16 May 2016.