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Designing a blackboard for a 5-inch screen

Most of our learners are on phones, on mobile data. That constraint shaped the entire interface.

TS

The Santi team

Product · 30 April 2026 · 8 min read

The first version of the board was designed on a 27-inch monitor. It was unusable on the device three quarters of our learners actually own.

The board scrolls, it doesn't shrink

Scaling a full board down to phone width makes handwriting illegible. Instead the board keeps its stroke size and pans to follow the active step, so the thing being explained is always the thing on screen.

Chat is a drawer, not a column

On desktop the transcript sits beside the board. On a phone it becomes a drawer that peeks the latest message and expands on tap, so the board never loses more than a third of the screen.

Designing for 3G

  • Strokes stream as vectors, a few kilobytes per step, not video frames.
  • Voice drops to an audio-only codec when bandwidth falls.
  • A lesson that loses connection resumes at the last completed step.

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