Consider going to gps guidance for planting straight corn rows. I have ordered the new Outback Guidance system which allows each pass to be straight independently from errors of the last pass. We know how longer marker errors magnify with each pass. I understand that you will plant straight enough to pull in with the combine any where without counting rows. It also allows you to plant contours by moving you over exactly one machine width from the first curving pass. Over hills expect the extra width to show up as wider than the normal row as it is more feet across the hill than it is across the flat. like wise use it to spread fertilizer, spray and drill.look at outbackguidance.com.