In the case of a center pivot irrigator, it is preferable that the irrigator travels around a stationary temporary reference member, the reference member being temporarily located in a hole in the ground and including ground engageable anti rotation means which enable the reference member to be fixed relative to {HEAD ~ motion} of {TAIL ~ the carriages} for reference purposes 
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In the case of a center pivot irrigator , it is preferable that the irrigator travels around a stationary temporary reference member , the reference member being temporarily located in a hole in the ground and including ground engageable anti rotation means which enable the reference member to be fixed relative to { HEAD ~ motion } of { TAIL ~ the carriages } for reference purposes
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