---
name: Split-flap animation
slug: split-flap-animation
category: motion
status: published
created: 2026-08-21T00:00:00.000Z
modified: 2026-08-21T00:00:00.000Z
definition: A digit or letter changing by flipping through every character
  between the old value and the new one, imitating the mechanical boards of
  airports and flip clocks.
aliases:
  - name: split-flap display
    source: community
  - name: flip clock
    source: community
  - name: Solari board
    source: community
  - name: flip digit
    source: community
  - name: flap animation
    source: community
tags:
  - retro
relations:
  contrastWith:
    - count-up-animation
    - typewriter-effect
  variantOf: []
  partOf: []
  seeAlso: []
implementations: []
sources:
  - title: "Wikipedia: split-flap display"
    url: https://en.wikipedia.org/wiki/Split-flap_display
  - title: "Design engineering: a split-flap display component"
    url: https://hello-mat.com/design-engineering/component/split-flap-display
demo: inline
exhibit: false
useWhen: a changing value should read as mechanical rather than digital
---

The original is a machine. A split-flap display holds a stack of hinged cards on a drum, each card
carrying the bottom half of one character and the top half of the next, and a motor turns the drum
until the right card is at the front. Because the drum can only turn one way, getting from O to L
means passing through every letter in between, which is why an airport board clatters through
twenty-odd characters to change one destination. The boards made by Solari di Udine, drawn by the
architect Gino Valle, made that clatter part of what a railway station sounds like, and the effect
survives in software purely as an imitation of a constraint no software has.

That is the whole point, and it is worth being honest about. A split-flap animation is slower than
simply writing the new value, it delays the information by a second or more, and the delay buys
nothing except the feeling that something physical has committed to an answer. Where that feeling
is the product, a countdown to a launch, a scoreboard, a clock on a wall display, it earns its
keep. Where the number is being read for work, it is friction dressed as craft. The tell for
whether it belongs is whether anyone would mind waiting for it.

Two neighbours share the mechanics. [Count-up animation](/count-up-animation) also runs a value
through intermediate states, but it interpolates a quantity, so the numbers it passes through are
arithmetic and the last one is the answer. A split flap passes through characters that mean nothing
at all, because they are positions on a drum rather than values. And the flipping itself is a
[stepped animation](/stepped-animation): a fixed number of discrete positions with no interpolation
between them, which is why a smoothly morphing flap looks immediately wrong.

Three details separate a convincing board from a novelty. Every cell holds a fixed width, so a
board reflowing mid-flip destroys the illusion of a physical frame and shifts the layout at the
same time. The cells start in sequence rather than together, left to right, because a real drum
takes a moment to receive its instruction and a board flipping in perfect unison reads as a screen
pretending. And the distance has to be capped or the slowest character sets the pace for the whole
board, which is how a charming effect becomes a five second wait. Under a reduced-motion preference
the value should simply be there, since the letters in between were never information.