Letter from Yervant Terzian, Assistant Director, Mr John M Payne, National Radio Astronomy Observatory, Edgmont Road, Charlottesville, Virginia Concerning the positioning of the feed structure at Arecibo, which he certainly thinks that a very possible solution for positional accuracy is of the order of 10". Has discussed this problem with Professor Gold, who thinks that the suspended structure at Arecibo is very stable, and when the new high accuracy tracks are installed the system should be capable of positional accuracy of the order of 10" (about 3 mm on the tracks.) In case their expectations do not come true they will look to other solutions. In any event Payne is thanked for his co-operation and they will keep in mind that he is the expert in 'sensing positions with infrared beams'. 26 January 1971