I have a loup monitor system that counts seeds. It is very accurate in soybeans. Pretty good in wheat. It monitors every row for blockage and has 4 rows monitored for seed counting. 30 ft air drill.
We have a great plains drill also we put a dickey john moniter on it with sencor 1 high rate cells on each end (2) on a 15 ft drill. It works very well once you get the reading you want we shoot for about a 400 reading on the timed count gets us the population we are looking for may take some tweeking but once you get used to it it works great set it on the first or second round and go like hell!!!