The Proportional Caliper is an essential instrument for quickly assessing the percentages of flat and elongated particles in coarse aggregates measuring 3/8" (9.5 mm) or larger. The Proportional Caliper is designed for efficiency, with a sturdy 6" x 16" (152.4 x 406.4 mm) base plate and rubber feet to ensure stability during tabletop testing.

The Proportional Caliper is made of sturdy 7 gauge steel and coated for corrosion resistance, making it appropriate for use in a variety of situations. It provides for simple modifications with four preset ratios: 1:2, 1:3, 1:4, and 1:5, which suit to various testing requirements.

To determine the shape of a flat particle for size, place the particle in the larger end of the caliper and tighten the pivot screw. Check the same particle using the smaller measuring end of the caliper without changing it. If the particle fits inside the smaller space, it is considered flat. The steps for determining elongated particles are the same. If the particle is greater than the small measurement in both cases, it is not considered flat or elongated.

The Proportional Caliper is used for compliance testing, ensuring optimal material performance, and avoiding difficulties during consolidation. The Proportional Caliper's combination of precision engineering and sturdy construction makes it an essential component to any testing laboratory, allowing for quick assessments of aggregate quality for construction and engineering projects.