5-Round Precision Test
Can you set the angle to exactly 90 degrees?
Rotate the adjustable blade until you believe it forms a perfect right angle. Then drop the engineer's square and measure your error in tenths of a degree.
All measurements remain in this page and vanish on reload.
Drag with touch or mouse. With the control area focused, Arrow keys (Shift for micro-step) and Spacebar work too.
5-Attempt History
Where did your eyes drift?
The center yellow line marks 90.0°. Each plotted marker reveals the measured angular error.
- Not attempted
- Not attempted
- Not attempted
- Not attempted
- Not attempted
Squareness Profile
Completed Series Results
- Mean error
- 0.0°
- Best attempt
- 0.0°
- Directional bias
- 0.0°
- Oblique penalty (45°)
- 0.0°
The oblique penalty compares two single attempts (|error at 45°| − |error at 0°|) and can come out negative.
Neurobiological Basis
Why do right angles degrade on obliques?
Primary visual cortex (V1) responds more strongly to horizontal and vertical orientations than to obliques; imaging shows a larger response, explained either by stronger neural gain or by a greater number of neurons (Furmanski & Engel, 2000). Documented in neurobiology as the oblique effect (Appelle, 1972), this neural anisotropy causes angular discrimination accuracy to drop substantially when references tilt along 45-degree diagonals.
Workshop squares conforming to DIN 875/0 allow, on a 150 mm blade, a perpendicularity deviation of 8 micrometres — about 0.0031°. The unaided eye distinguishes a daylight gap as narrow as 2–3 micrometres; an error of a few tenths of a degree opens a gap of hundreds of micrometres (0.2° ≈ 520 µm over 150 mm), visible at once.
The 0.2° threshold for a “precision fit” and the workshop ratings are internal grades of this page, not trade benchmarks. The test measures visual estimation on a screen; it does not measure skill with physical stock at the workbench.