This device from wildco --also known as a gravel meter or pebble meter--is used to grade or measure gravel and cobble-sized bed sediments in the field. Your Cobble measurements will be far more accurate than using a ruler. Made of anodized Aluminum, it is lightweight yet strong, therefore easy to carry and use in the field. It incorporates 14 square holes of common sieve sizes (1/2 PHI unit classes) ranging from 2 mm to 180 mm. Measure up to 310 mm (in 10 mm increments) using the built-in scale. Dimensions: 13 1/2 inch x 11 inch (34.3 cm x 27.9 cm) meet usgs standards in Cobble size measurement 14 square holes in common sieve sizes lightweight construction for easy field use metric scale along one side