sweet corn plates

As CNKS mentioned, you will in actual practice never completely eliminate cracked seed or doubles. Take a sample of seed with you to plate supplier. Also take along a rubber band long enough to go around a seed plate. Visually find the plate that matches your seed. When you get down to 3 or 4 close possibilities, put the rubber band around plate and put some seeds in cells, behind rubber bands.

You may as well buy several plates as seed you get next year could be different size. That fact cant be avoided, growing plants go with the season. As CNKS said, "Until you get in actual field conditions, you will not be 100% sure plate size is correct." I have seen this same thing with grain corn and you had the seed plate numbers from supplier. These problems worsened after the introduction of air planters as well. Seed was sized far better back 40 years ago than it is today.

Back in my farming days I had two planters, one being an IH 4 row air planter and a 2 row 3 point John Deere. Often used that little plate planter in small fields, headlands or finishing off triangle shaped fields. Seed sizing was a problem that increased over the years. It will never improve as none of the new planters require the seed as acurately sized. Precisely why old planters are cheap.

One other thing you can do as a final check is "test planting" on a hard surface (like the driveway). You should end up with a row of seeds laying on top of the ground that you can check for skips and broken seed. You need to run this test at the same speed you intend to run in the field. Sometimes you won't get skips at slow speed even if it skips at higher speed.

A master plate can help you determine the right plate.