# Can You Find the Center of the Circle?

A 5-round visual precision test: tap where you think the exact center lies across five geometric shapes on a drafting board, without a compass. A steel needle drops to measure your error in millimetres and compass bearing.

[Open interactive test](https://mariuscomper.uk/fara-compas/en/)

## How it works

1. Each round presents a distinct geometric shape (clean circle, solid disc, asymmetric visual mass, open arc, tilted ellipse).
2. Tap the board or navigate with arrow keys and press Enter to mark the center.
3. A compass needle drops onto the true mathematical centroid, and concentric tolerance rings measure radial error in millimetres.
4. After five rounds, a master polar reticle maps all five attempts, computing your average error, best attempt, and systematic directional bias.

## Why do we place the center too high?

The human visual cortex does not calculate abstract Euclidean centroids. In natural terrestrial environments, vision constantly surveys ground receding downward toward the horizon.

To compensate for this perspective, the visual system lifts the perceived center of two-dimensional shapes by 1.5% to 4.0% above the true geometric center. Most people tap the circle above the mathematical axis.

## Measurement and privacy

Coordinates are evaluated against standard CSS pixels (96 dots per inch, where 1 millimetre corresponds to approximately 3.78 pixels). All measurements remain strictly in volatile memory and vanish on reload.

Text and implementation: Marius Comper, 2 September 2026.