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A simplified one-page spreadsheet was developed for teaching the concepts and value of crop models for students in agricultural systems management and agricultural and biological engineering. This model, CROP, is much less complex, less accurate and less realistic than a real crop model. It uses only linear equations with some limits on allowable values. It is a "model of a model", designed strictly for teaching some of the major causes and effects in crop growth, the feedback processes, the dynamic processes, and a simplified concept of how a process-based crop model works. This spreadsheet illustrates how a model can be used for crop and machinery management. It makes calculations weekly, instead of daily, to save space on the screen. It illustrates interactions between variables. Crop models can be used by agricultural systems managers for strategic planning of the next year's crop, or for tactical day-to-day management of irrigation and fertilization. Crop models have been used to determine new machinery needs for the future, based on yields, maturity dates and field losses. This simple model helps students in management and engineering quickly grasp the overall concept of a crop model without understanding all the details of crop physiology.