Units

A unit is a representation of measurement. In STEP, a unit is an object that can be associated with attributes or LOVs (List of Values). A measurement stored as an attribute will typically consist of a value and a unit (or unit of measure).

The separation of the unit and the value of a measurement means:

  • The value part can be validated according to numeric criteria.
  • The value part can be searched and compared according to operators such as '>' and '<.' (Values for numeric searches with no units are assumed supplied in the default unit for the attribute. For example, if kg is the default unit for the Weight attribute, 'Weight = 1' will match '1 kg' and '1000 g'.)
  • It is possible to establish automated conversion between values of different units of measure.
  • More presentation options, e.g., in 'specifications tables.'
  • Consistency can be enforced in the use of units.

Note: Units can be applied to attributes and/or LOVs of all validation base types except: Condition, Text, Date, 'ISO Date', 'ISO Date and Time', URL, and Regular Expression.

A unit is housed in a unit group and can include a unit conversion. Both of these are discussed below, as well as information for maintaining each of these elements.

Unit Groups

A unit group is a grouping of compatible units. It contains units that apply to the same measurement. This makes it possible to establish rules for conversion between units within the group.

Unit groups are available for attributes and List of Values (LOVs). Examples of unit groups and units are included in the following table.

Unit Group

Units

Temperature
  • Celsius
  • Fahrenheit
  • Kelvin

Dimension
  • mm
  • cm
  • meters
  • inches
  • feet
  • yards

Volume
  • cm3
  • m3
  • inch3

For example, if the unit group 'Dimension' has been linked to the attribute RopeLength, then the units mm, cm, meters, inches, feet, and yards can be applied to the value of RopeLength.

Unit Conversions

A unit conversion specifies the rules for conversion from one unit to another. One of the units must be a base unit. It is possible to define a conversion rule between two compatible units. Unit conversions are used when, for example, exporting data and when searching for Attribute Values. Examples of unit conversions are included in the following table.

Time(s)

ID

Name

Conversion

Second

unece.unit.SEC

s

 

Minute

unece.unit.MIN

min

(1 min = 60 s)

Hour

unece.unit.HUR

h

(1 h = 3600 s)

Day

unece.unit.DAY

d

(1 d = 86400 s)

Note: The system will normally include a pre-defined set of units according to UN/ECE standards. New units may be added if this standard does not provide a suitable unit. However, inspect the available units carefully before doing so. The pre-defined units are also provided with standard unit conversions

Conversion Factor and Conversion Offset

A unit conversion is specified in terms of a conversion factor and conversion offset.

Note: A conversion factor and conversion offset must be typed with minimum of one decimal and must never be empty. Type '0.0' to indicate a factor or offset of '0' (zero).

The following example shows the conversion rule for temperature conversion from Celsius into Fahrenheit using the formula: Temperature Fahrenheit = (1.8 * Temperature Celsius) + 32

Unit

Unit Conversion Factor

Conversion Offset

Fahrenheit (base unit)

 

 

Celsius

1.8

32.0

As an explanation of this example, to convert a Celsius temperature of 100 degrees into degrees Fahrenheit:

  1. Multiply the Celsius temperature reading by 1.8 to get 180.
  1. Then add 32 to 180 and get 212 degrees Fahrenheit.

Additional Information

For information on creating or deleting the elements included in a unit, refer to the following topics: