# Code Table for Unit mappings

A Code Table for Unit mappings provides a mapping of input units to output units for quantitative data.

The unit conversion process consists of the following steps:
- Read source unit.
- Read target unit.
- Convert source unit to target unit.

Conversion between units is defined as follows:
`Target unit = source unit * conversion factor + offset`

Except when converting between temperature units, offset equals 0 in most cases.

An example of Celsius to Kelvin conversion:
 1. Given 37 Celsius
 2. Expect Kelvin
 3. 37 * 1 + 273.15 = 310.15 K

An example of Celsius to Fahrenheit conversion:
 1. Given 37 Celsius
 2. Expect Fahrenheit
 3. 37 * 1.8 + 32 = 98.6 F

A Code Table for Unit mappings MUST include the following attribute:
- entries

The “entries” attribute is a map of key-value pairs, where the key denotes the conversion from source to target (e.g., "m->mm" or "deg_c->deg_f") and the value contains the conversion factor and the offset.

All units and unit prefixes follow the “Data Protocols Lightweight Standards and Patterns for Data” [BER2013] proposal for describing units associated with numeric quantities.

{
   "entries":{
      "m->mm":{
         "cf":1000
      },
      "m->yd":{
         "cf":1.0936133
      },
      "deg_c->deg_f":{
         "cf":1.8,
         "o":32
      }
   }
}

Example 23. Code snippet for a Code Table for Unit mappings.

Code Table for Unit mappings is in denormalised form, meaning that the conversion between units and unit prefixes is pre-defined for all standard unit conversions for maximum efficiency.