Base [StructureDefinition](/content/docs/api/fhir/resources/structuredefinition/index.html) for [Duration](/content/docs/api/fhir/datatypes/duration/index.html) Type: A length of time.

## Elements

| Name       | Required | Type                                              | Description |
|------------|----------|---------------------------------------------------|-------------|
| id         |          | string                                            | Unique id for inter-element referencing<br>Details<br>Unique id for the element within a resource (for internal references). This may be any string value that does not contain spaces. |
| extension  |          | [Extension](/content/docs/api/fhir/datatypes/extension/index.html)[] | Additional content defined by implementations<br>Details<br>May be used to represent additional information that is not part of the basic definition of the element. To make the use of extensions safe and manageable, there is a strict set of governance applied to the definition and use of extensions. Though any implementer can define an extension, there is a set of requirements that SHALL be met as part of the definition of the extension.<br>There can be no stigma associated with the use of extensions by any application, project, or standard - regardless of the institution or jurisdiction that uses or defines the extensions. The use of extensions is what allows the FHIR specification to retain a core level of simplicity for everyone. |
| value      |          | decimal                                           | Numerical value (with implicit precision)<br>Details<br>The value of the measured amount. The value includes an implicit precision in the presentation of the value.<br>The implicit precision in the value should always be honored. Monetary values have their own rules for handling precision (refer to standard accounting text books). |
| comparator  |          | code                                             | < | <= | >= | > - how to understand the value<br>Details<br>How the value should be understood and represented - whether the actual value is greater or less than the stated value due to measurement issues; e.g. if the comparator is "<" , then the real value is < stated value. |
| unit       |          | string                                          | Unit representation<br>Details<br>A human-readable form of the unit. |
| system     |          | uri                                             | System that defines coded unit form<br>Details<br>The identification of the system that provides the coded form of the unit. |
| code       |          | code                                            | Coded form of the unit<br>Details<br>A computer processable form of the unit in some unit representation system.<br>The preferred system is UCUM, but SNOMED CT can also be used (for customary units) or ISO 4217 for currency. The context of use may additionally require a code from a particular system. |

- [Elements](/content/docs/api/fhir/datatypes/duration#elements/index.html)