Piston meters are far superior to gear meters when measuring the flow rate of low viscosity fluids. The clearance between a rotating gear and the meter body is usually 5 times larger than the clearance around the pistons used in a Max meter. This larger internal leakage is the main reason that gear meters are calibrated using a 20 or 30 cps fluid. The operating range of a gear meter might be specified as 100:1 on a 20 cps fluid, but it will only maintain its accuracy over a 4:1 range when measuring 1.4 cps viscosity AdBlue. Applying a gear meter outside of its range of ability is not necessary. The emission testing industry has found a better alternative in the piston style meter. Compare the Model P213's calibration done on 3 cps fluid against any gear meter, including ours, and you'll see why gear meters are no longer specified for high accuracy measurements of fuels and diesel exhaust fluid.