Downpressure for corn planting?

Where I farm our soils can change a bunch of times in one field so getting the right downpressure is a tuff thing to do across the whole field. An active downforce system is almost a must if you want to be close. In most active systems you are able to set the margin that you are shooting for. Im guessing that the 140-180 you are referring to is margin but not sure. Margin is the weight that is left over between the gauge wheels and the ground after the seed is placed at the depth you are shooting for. In a perfect world margin would be between 1 and 5 lbs because your planter unit did it’s job the seed is at the right depth and your guagewheels are not causing compaction right around the seed your are trying to get to germinate. Now 5 lbs wound be great for Margin but you need to have a little freeboard on those gauge wheels in case you get in to hard ground so usually we shoot for 50 margin in fields that are soft and 75-100 in fields that have very dry or ruff spots In them that you do not want to have any shallow seeds planted. For guys that do not have an active system you need to plant in a part of your field that you know is harder than the rest and keep increasing downpressure until you can just barely turn your gauge wheel with your hands. Keep in mind if you have three bu hoppers you will not want to do this with them completely full because when they get empty now you prob don’t have enough downpressure again. Hope this helps