From the site:
"The ARC-SET's transparent body allows you to see the bubbles from virtually any vantage point (for alignment of Dishes which are in creatively inconvenient locations). There are transverse bubble vials fixed in each end to guide you in measuring the steepest slope angle of any inclined surface. Your ARC-SET can be pre-set for your 50-mile territory, based on our computer's "Optimum 'Polar' Mount Analysis". You can easily re-set it for alternative locations. Loosen the slotted screws to change its settings. With the screws loosened, the adjustable level vials turn easily. Put your ARC-SET on a trustworthy "Mother Dish", in the alternative location, that is satisfactorily on ARC (with its Feed properly laterally focused), center the AXIS, then ZENITH, and finally the EXTREME bubbles, and tighten the slotted screws (they go metal to matal, to lock the bubbles firmly without risk of pulling out threads). Your ARC-SET will duplicate that "Mother Dish" exactly and within a 50-mile radius, it will put all the new Dishes on the Arc just like it. Be sure to set it back, from one of your previously set local Dishes, when you return home."
Extended Arc-Set Information
"The ARC-SET's transparent body allows you to see the bubbles from virtually any vantage point (for alignment of Dishes which are in creatively inconvenient locations). There are transverse bubble vials fixed in each end to guide you in measuring the steepest slope angle of any inclined surface. Your ARC-SET can be pre-set for your 50-mile territory, based on our computer's "Optimum 'Polar' Mount Analysis". You can easily re-set it for alternative locations. Loosen the slotted screws to change its settings. With the screws loosened, the adjustable level vials turn easily. Put your ARC-SET on a trustworthy "Mother Dish", in the alternative location, that is satisfactorily on ARC (with its Feed properly laterally focused), center the AXIS, then ZENITH, and finally the EXTREME bubbles, and tighten the slotted screws (they go metal to matal, to lock the bubbles firmly without risk of pulling out threads). Your ARC-SET will duplicate that "Mother Dish" exactly and within a 50-mile radius, it will put all the new Dishes on the Arc just like it. Be sure to set it back, from one of your previously set local Dishes, when you return home."
Extended Arc-Set Information