## 4.2.15.12  Units of Measurement
Many business applications use units of measurement in their business processes. To standardize these processes, you need a central maintenance of units and related dimensions. Beside that, there's a business need for conversion between different units.
We provide a subset of common standardized units, dimensions, and ISO codes for use as predelivered content. In addition, you need to define customer-owned units and dimensions in customer applications.
## How are Units and Dimensions Linked?
Units are related to a dimension. In each dimension, a unit is defined as an SI unit (International System of Units). This is the basis for the conversion from one unit to another.
## Warnings
Changing a unit of measurement (UoM) may have an impact on your applications, especially on the critical fields.
UoMs are used across applications. An initial set of UoMs is delivered in the system. You can adapt UoMs as per your requirements. Be aware that by adding, changing, or deleting the customizing, you are changing the initial set of UoMs delivered in the system.
##  Caution
Pay special attention if UoMs are already saved in transactional data of productive business processes. Changes of the fields marked as critical can result in serious inconsistencies.
We strongly recommend that you do not delete any dimensions, ISO codes, and units that are already defined in the system.
## Critical Fields
| Critical Fields For...   | Critical Fields                                                                                                                                                                                                                                                   |
|--------------------------|-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| Dimensions               | SI Unit The SI Unit is the base unit of a dimension for conversion. By changing the base unit, the conversion will be performed on a different base unit defined.                                                                                                 |
| Units of Measurement     | • Numerator • Denominator • Exponent • Additive Constant • ISO Code • Primary Code                                                                                                                                                                                |
|                          |  Caution Numerator, denominator, exponent, and additive con- stant define the conversion factor with respect to the SI units. Any changes of the conversion factor will change the output result of a conversion between units under the same dimension.         |
|                          |  Caution Changing the ISO code and primary code may have an impact on applications. For example, ISO codes are used as normed measurement unit IDs for electronic data interchange (EDI). If no ISO code is assigned to a unit, you may encounter issues in EDI. |
## Related Information
Maintaining Dimensions [page 1519] Maintaining Units of Measurement [page 1529] Retrieving Standard Units of Measurement [page 1541] Conversion Functions for Units of Measurement [page 1543]