A unit of measure list type (UoMListType) is a special type of enumerated list with additional semantic information.
Conversion Factors
Each enumerated entry in the unit of measure list has conversion factors to convert from the SI units for that list to the specific units of measure selected by the user. In the schema, a UoMEnum contains two conversion factors: a multiplier (A) and an addend (B). These conversion factors are used to convert the value to SI units. For example, the given unit (x) is multiplied by A and then B is added to that value to determine the SI value (y = Ax + B).
A UoMListType is a composition of enumerated unit of measure entries. One entry in every unit of measure list has a relationship of HasDefaultSI with the UoMListType, which means that the entry is the default SI unit of measure for the list. For example, in the TimeUoM list, "s" (seconds) is the default SI unit of measure for time.
Other Characteristics of UOM Lists
A unit of measure list may have an associated enumerated list that identifies the possible conditions for that unit of measure list. For example, the pressure unit of measure list has an associated enumerated list that identifies whether the pressure value is absolute or gauge (@ Gauge).
A property definition that is typed as unit of measure has a double precision floating point value in the SI unit for that list. It can also have a preferred display unit of measure, a number of significant digits, and uncertainty.