CRITICAL DIFFERENCE BY MURRAY LEINSTER [Transcriber's Note: This etext was produced from Astounding Science Fiction, July 1956. Extensive research did not uncover any evidence that the U.S. copyright on this publication was renewed.] I Massy waked that morning when the only partly-opened port of his sleeping-cabin closed of itself and the room-warmer began to whir. He found himself burrowed deep under his covering, and when he got his head out of it the already-bright room was bitterly cold and his breath made a fog about him. He thought uneasily, _It's colder than yesterday!_ But a Colonial Survey officer is not supposed to let himself seem disturbed, in public, and the only way to follow that rule is to follow it in private, too. So Massy composed his features, while gloom filled him. When one has just received senior service rating and is on one's very first independent survey of a new colonial installation, the unexpected can be appalling. The unexpected was definitely here, on Lani III. He'd been a Survey Candidate on Khali II and Taret and Arepo I, all of which were tropical, and a Junior Officer on Menes III and Thotmes--one a semiarid planet and the other temperate-volcanic--and he'd done an assistant job on Saril's solitary world, which was nine-tenths water. But this first independent survey on his own was another matter. Everything was wholly unfamiliar. An ice planet with a minus point one habitability rating was upsetting in its peculiarities. He knew what the books said about glacial-world conditions, but that was all. The denseness of the fog his breath made seemed to grow less as the room-warmer whirred and whirred. When by the thinness of the mist he guessed the temperature to be not much under freezing, he climbed out of his bunk and went to the port to look out. His cabin, of course, was in one of the drone-hulls that had brought the colony's equipment to Lani III. The other emptied hulls were precisely ranged in order outside. They were duly connected by tubular galleries, and very painstakingly leveled. They gave an impression of impassioned tidiness among the upheaved, ice-coated mountains all about.