While itself varying, such change must be taken into account when designing a system for overall behavior to stimuli or likely environmental conditions, and in particular the worst-case conditions encountered under the high stresses imposed near the limits of operability— for example, an air-cooled engine in a desert climate on a very hot day.
When developing a system that reacts to external influences or climate conditions, it's vital to account for fluctuations that may arise. This is especially pertinent when designing for scenarios where the system is subjected to extreme temperatures, such as an air-cooled engine operating in a sweltering desert on an extremely hot day.