Specifications:

rigid, L-shaped piece of laminated plastic 1 mm thick

millimeter markings accurate to 0.1 mm or better

overall size is 105 mm x 105 mm (about 4" x 4")

gray areas have a reflectance value of approximately 18%

alternating black and white bars (1 cm) to permit measurements from grossly over- and underexposed photographs

The incorporation of three circles is useful in helping to compensate for distortion resulting from oblique camera angles.

The graduations are all metric, except for the width of the legs which are 1-inch wide. The 1-cm division lines are traced and extended across the photographic print to grid an image.

Measurements within the image are then made relative to these inscribed 1-cm grid lines to compensate for any distortion resulting from non-parallelism between the film and the object planes.

For an in-depth technical description on the use of this scale, read the article by William G. Hyzer and Dr. Thomas C. Krauss in the Journal of Forensic Sciences, Vol. 33, No. 2, March 1988.