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, which was introduced to the market last week, the Digirod. It can emulate various grade rods, including direct elevation rods, cut/fill rods and inderect reading rods. Users must site a rotating laser beam in the device's reception window and then shoot a laser distance meter mounted on the Digirod to the bottom of, say, a trench. These measurements compute the grade.