ABFO #2 Scale
Definition
American Board of Forensic Odontology scale number 2. A right-angle (L-shaped) ruler with three circles at known spacing, used to correct perspective distortion in close-up evidence photographs. Placed in the same plane as the evidence.
- Shape
- L-shaped (right-angle) ruler
- Distortion check
- Circles that appear as ellipses if camera angle is off
- Exposure aid
- Black, white and grey reference bars
- Issuing body
- American Board of Forensic Odontology
- Placement rule
- Same plane as the evidence, parallel to camera back
Common questions
Why does the scale use circles rather than only straight lines?+
A circle photographed off-perpendicular distorts visibly into an ellipse, giving the examiner a quick visual check of camera angle error that a straight ruler cannot show.
What happens if the scale is not placed in the same plane as the evidence?+
Distances measured on the injury will be miscalibrated, since anything above or below the scale's plane is foreshortened differently by the camera, producing inaccurate size measurements.
How is this different from using a plain ruler in photographs?+
A plain ruler only calibrates linear distance along one axis, while the ABFO scale's circles and bars also flag perspective distortion and let the lab correct exposure and color during analysis.
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