Correction services are used to improve the accuracy and quality of the location data provided by receivers using satellite positioning services, including GPS.  Without correction, your receiver could direct you to the nearest Walmart, but wouldn’t be very accurate at guiding your tractor down the field.  Most corrections services use land-based towers as a reference in addition to algorithms that help filter out errors.  Satellite based corrections, such as Trimble RTX, use large towers across the continents to improve accuracy and availability, so the grower doesn’t have to worry about radios and communications.  Adding the right correction service to your receiver will result in better performance of all the precision ag tools on your farm.  More accuracy will cost you more money up front but will also deliver less frustration with operations in the field.