# Can you set the angle to exactly 90 degrees?

A 5-round precision angle test on [mariuscomper.uk/fara-echer/en/](https://mariuscomper.uk/fara-echer/en/).

## How it works

1. Rotate the adjustable tool blade against a fixed baseline until you believe it forms a perfect right angle.
2. Press "Verify angle". A DIN 875/0 engineer's steel square drops onto the corner and measures your exact deviation in tenths of a degree.
3. Complete 5 spatial challenges (0° horizontal, 25° incline, 45° diagonal, 120° inverted joint, 70° steep pitch).

## Calculated results

- Mean absolute error from 90.0°;
- Personal best attempt;
- Directional bias (tendency towards acute or obtuse angles);
- Oblique effect penalty (accuracy drop on 45° diagonal vs 0° horizontal);
- Workshop mastery rating (from *Master Craftsman* to *Broad Angle*).

## Neurobiological basis

Primary visual cortex (V1) contains a higher density of orientation-tuned neurons for cardinal (horizontal/vertical) axes than for obliques (Appelle, 1972). Right-angle estimation degrades noticeably when reference frames tilt along 45-degree diagonals.