20/20 will react fast enough.  This is my second year and my new RX writer put one acre squares in the middle of some zones as checks.  I really like the idea better than what I did last year, which was to go to manual an pull a straight rate across the field.  I usually remembered.  It also proved to be unreliable with a grain cart weight if we were crossing multiple zones.  I thought that would be better, but really I was compare 2 things at a time, instead of one against another.  With the blocks we will be able to compare rates so we know if they are using the correct ones.  At least for that year.