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NISO's 1995 guidelines for preserving paper records set narrow parameters for changes in temperature and relative humidity for existing library buildings. Although these guidelines are feasible in new structures designed to maintain stable environmental conditions, they are impractical for older facilities such as the University of Colorado's Norlin Library, a 65 year-old building in a semi-arid climate. Because Norlin's HVAC system uses evaporative cooling, its relative humidity is impossible to stabilize. Yet its collections are well preserved. Damage has occurred only to one collection—and only during a period when humidity, though higher than normal, was relatively stable. Norlin's experience reinforces the need to interpret the NISO's guideline for relative humidity, taking into account the different types materials within the collections as well as the building's HVAC system.