rollingdigit

Rollingdigit is a term used to describe a digit in a counter or display that cycles through a fixed set of values as counting proceeds. In mechanical or digital counters, each digit occupies a position with a defined maximum; when an increment causes a digit to reach its maximum, it rolls over to the minimum value and a carry is generated to the next more significant position. The rolling action is often implemented as a wheel or segment that visually advances through values, typically from 9 to 0 in base-10 systems.

In user interfaces, rolling digits refer to animations where the next numeral slides or rotates into view to replace the current one. This effect is common in clocks, countdown timers, scoreboards, and other numeric displays, chosen for readability and a tactile sense of progression.

Mathematically, rolling digits are described by modulo arithmetic. A k-digit rolling counter tracks values modulo 10^k; each increment updates the least significant digit and propagates carries when a lower-order digit overflows. This framework underpins odometers, digital counters, and base-n counting schemes.

Variants of rolling digits include vertical, horizontal, or carousel-style displays, as well as mechanical rolling disks and LCD-style segment animations. While the term is not tied to a single standardized technology, it is often used to describe both the underlying carry behavior and the visible rolling effect in numeric displays.

See also: odometer, modulo arithmetic, counter, digital clock, rolling animation.