Performing arithmetic operations on measurements with mixed units of measures in the metric system requires the same care we used in the U.S. system. Many measurements in the United States are made in...Performing arithmetic operations on measurements with mixed units of measures in the metric system requires the same care we used in the U.S. system. Many measurements in the United States are made in metric units. We make conversions between the systems just as we do within the systems—by multiplying by unit conversion factors. The U.S. and metric systems use different scales to measure temperature. The U.S. system uses degrees Fahrenheit. The metric system uses degrees Celsius.