This calculator evaluates a selected right-triangle clearance proxy: θ=atan(c/L), angular error in degrees and arcminutes, and transverse drift D·tanθ=Dc/L. It does not predict the measured parallelism of a complete ruler.
Slotted Parallel Ruler · Selected Clearance Proxy
Explore an exact selected clearance triangle and its transverse projection without treating it as a complete ruler tolerance model.
Equation Used
- Clearance c is treated as the opposite side of a right triangle with adjacent side L.
- Drift is the transverse projection of that selected angle over D.
- The inputs do not determine the full pin-slot or crossed-link constraint geometry.
- Contact state, tolerances, stiffness, wear, handling, loads and safety are excluded.
The angle inset is enlarged only for legibility; all reported values use the unamplified selected ratio.
Selected clearance triangle
The ruler uses two equal crossed bars, pivoted together at their centers. Each bar has one end pivoted to a blade and the other sliding in a slot in the opposite blade. The blades remain parallel as their separation changes. The separate calculator treats clearance c as the opposite side and effective length L as the adjacent side of a right triangle; its angle inset is enlarged for readability.
What the calculator determines
Select clearance, effective length and walk distance. The calculator reports the exact proxy angle, arcminutes, drift and dimensionless clearance ratio.
Exact proxy identities
θ=atan(c/L); arcmin=60θdeg; drift=D·tanθ=Dc/L; ratio=100c/L.
Selected-input example
For c=0.05 mm, L=30 mm and D=600 mm, θ is about 0.0955°, 5.73 arcminutes, and the selected drift proxy is exactly 1.00 mm.
Proxy, not tolerance prediction
Actual error depends on pin diameter, slot width and angle, contact side, number and arrangement of links, preload, wear distribution, blade stiffness and handling. Those details, loads and safety are excluded.
Questions
Why use atan instead of c/L?
atan(c/L) is the exact angle of the disclosed right triangle; c/L is only its small-angle approximation in radians.
Does the drift predict a charting error?
No. It is the transverse projection of the selected proxy angle over distance D, not a calibrated instrument-error model.
References & Further Reading
- Wikipedia contributors. Parallel rulers. Wikipedia
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