When a laser is to be set on a flat surface where the laser beam is not centered in the pipe, use the Spectra 1237 Heavy Duty Trivet Plate. Using this system, the elevation of the laser beam can be set by either measuring down from a grade offset hub outside the trench or up from the floor of the manhole to the beam.
The 1237 is a metric version of the invert plates while the 1230 follows the imperial unit. Plus, it is a one-piece cast aluminum support plates that provide automatic self-centering of the Laser in 10 inches (250 mm), 12 inches (300 mm), or 15 inches (400 mm) pipe diameters.
The invert plates are used along with the 1239 Universal Fixed Pole for setups on the manhole bottom, outside of the manhole or in pipes larger than 15 inches (400 mm) diameter.