Abstract: A planter monitor system monitors, measures and displays a plurality of planter performance parameters. The system includes a display console, a plurality of row unit modules and a plurality of seed sensors. The system can be used with a wide variety of planters made by different manufacturers and on many different planter types. The system can accurately monitor a wide variety of seed types (e.g. both small and large) and a wide variety of seed planting rates (low and high) and any combination thereof which can occur within the wide scope of seed planting. The system calculates an error rate from a set of data, in graph form, representing experimentally determined actual seed rates versus seed rates as would be measured, thus allowing the operator to optimize seed population and distribution by adjusting the speed of the planter apparatus and/or the seed distribution system.