Simplify the following text for a Grade 5 native English-speaking person.
Original: French decimal time is sometimes called `` metric time '' because it was introduced around the same time as the metric system and both were decimal , but it was not part of the decree creating the original metric system and its units were named for the hour , minute and second , instead of using metric prefixes .
Simplified: Metric time is a way of measuring how long a period of time is using the metric system . The metric system uses the second as a main unit of time .