Courtesy Trimble Trimble's Digirod can measure grade from a rotating laser without ever touching the ground. From the "groma" with its right angles and plumb bobs used 3,000 years ago to modern-day grade rods, surveyors have been using some type of rod in their work. A new grading device claims to eliminate the need for grade rods when checking grades with a rotating laser. It compounds a laser distance meter, laser receiver, tilt sensor and digital readout to get grade readings without touching the ground at tilt angles of up to 30 degrees.Trimble Inc., Sunnyvale, Calif., calls its grading instrument,
Arch dams, classically curved monoliths situated in narrow valleys, are not as common as other types of dams, such as embankment dams and gravity dams. ENR takes a look at some of the biggest arch dams in the world, both completed and under construction.