if it was trimbles system, ya it's not so good, they have some work to do, and the  loupe system I had was a joke. the problem with ag leaders system is overall bu. seem to be pretty close, but hybrid variance's can be quite large.  you can make some serious mistakes if you are using ag leaders system for hybrid comparisons alone.  heck I know what the total field has done when it's hauled to town, don't need a yield monitor for that.  what I need to know is where the good and bad spots are in the field, so I can address them appropriately.     what I mean is this; if my yield monitor is off 3% total, i need it to be off 3% when 100bu. acre corn is coming in, 3% when 280 bu corn is coming in, and everything in between. yield maps are practically useless if this kinda tolerance is not held.  i've seen enough ag leader maps that come from machines that are calibrated to the nth degree that need a lot of data normalization.