Why do we need zeroing?

Moving the large amounts of dirt involved in landforming is costly. So you want to do it right to minimize rework. To do that, you want to get the heights right, or else you will end up needing more dirt, or having excess dirt. However, the GPS on an implement cannot be placed right at the dirt moving edge. It is offset, and base stations can be moved, and GPS can sometimes experience drift. To avoid these issues, many designers will survey benchmarks that their work is referenced to. These benchmarks are crucial to getting your height right. When you place your implement's blade on a benchmark and zero, you are matching the digital design to the local reality.