Because of where the Dish platform is on top og BBC Scotland, and it is so far from the Dish build area the Crane had to be a 850 tone crane with a 45m Fly Jib to get the reach although its a 850 ton crane it wont lift anything that weight at long reaches it is greatly reduced the further away you get from the Vertex point on the crane.
This Video shows from down in the Dish build area that the first crane brought to site was miss calculated as we couldnt get within 27m of where we wanted the dish installed, the first crane was a 500 ton crane with 25m of Extended Fly Jib.