Mackenzie investigates how the volume of gas inside a balloon changes as the temperature of the gas changes. She takes an inflated, sealed balloon from a freezer and uses a string and a meterstick to measure the balloon’s circumference. She moves it to a sunny window for 15 minutes. Then she measures the circumference with a tape measure. She records these measurements in a data table. Mackenzie realizes that she made a mistake in her procedure. Which claim describes what was wrong with her procedure?