First it doesn't matte when u calibate the Ag.eader, u can take it out of the box and harvest 3_4 of your crop and not calibrate it, because when you do calibrate it, it calibrates back too. Also trimble is bout the best there is when it comes to s GPS satilites. That is their biz and they have contracts for GPS with many differant compaies. I also belive the agleader is easyier to use. But that is just my thought. Also it is made to use with differant eq. And to beable to hook up to ravens and other monitors. And the tech soport behind an agleader is second to none. These have been my experinces. Our neibors bought a greenstar and wishes he would of went with the Adleader.