A numerical input to a computer, such as an input of runway altitude to an aircraft control system, is controlled by a switch having five positions as follows: "off" for maintaining the current value, "slow increment" for increasing the value slowly, "fast increment" for increasing the value more quickly, "slow decrement" for slow decrease in the value, and "fast decrement" for faster decrease in the value. A processor monitors the current switch position. Depending on the period that a particular position is selected, the value fed to the control system and shown on a display can be "bumped" unit by unit (small units for a "slow" selection, and large units for a "fast" selection) or scrolled up or down at a rate which accelerates. Bumping is achieved by toggling the knob quickly from the off, or the next closest position, to the desired slow or fast position. Scrolling or "continuous slew" is selected by maintaining the switch in the desired slow or fast position.
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