An International Harvester No. 1 check-row corn planter.
As can be seen in this illustration of how to lay out check wire, the wire couldn’t be pulled absolutely taut but had enough slack left to allow it to follow the planter when close to the end of the row.
A check-row planter equipped with side-mounted wire reel, disc row markers and a fertilizer attachment.
A planter check head showing how (assuming the planter is moving from right to left), as the wire slides through the fork (b), the button in the wire (a) catches the fork and pulls it to the rear, opening the valves under the planting units and dropping a hill of seed.