Units of measure are identical, so that a count of them is a measure.

• Applies understanding of identical units to "units of units." Can effectively translate between the two.
  
• Understands total length, partition of total but mixes unit-of-units and unit. For example, creates a composite unit of 5 original units, but reports a distance of 11 original units as "3" meaning 2 unit-of-units and 1 original unit.
  
• Forms composite units, "unit-of-units."
  
• Partitions units into n congruent parts.
  
• Understands need for identical whole units but does not extend this to partitions of units. (Lines to label partitions are often drawn randomly)
  
• Understands need for identical units: Employs identical units when constructing measurement tool. Justifies by appeal to the sensibility of the resulting count as an accumulated quantity. If units are not identical, the count explicitly labels each type of unit.
  
• Elementary recognition that identical units are required-in plane of activity or by appeal to ritual. For example, paces with own feet to measure or says that inches are all alike but cannot justify their virtues. But when constructing a measurement tool, does not generate identical partitions.
  
• Counting space but sees no need for identical units. For example, mixes different units of measure and simply counts all as the measure of the length.