> For the complete documentation index, see [llms.txt](https://docs.snomed.org/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.snomed.org/snomed-ct-user-guides/snomed-ct-browser-guide/how-to/compare-historical-versions-of-a-snomed-ct-concept.md). # Compare historical versions of a SNOMED CT concept | Steps | References | | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | --------------------------------------------------------------------------------------------------- | |

With the desired focus concept in the Concept Details panel, press :chevron-down: on the Perspective button in the header bar to see a drop-down options list of available perspectives:

|
| | Select `Comparing` to switch the presentation to `Perspective: Comparing`. |
| |

Perspective: Comparing maintains the browser header bar, but changes to show two side-by-side Concept Details panels, with a full-width Search panel below them.

When invoked with a concept already in the Perspective: Full Concept Details panel, the focus concept will be preserved in both Perspective: Comparing Concept Details panels.\

Panel sizes can be adjusted

The relative sizes of the three panels can be adjusted by pressing and dragging their gray border bars.

When comparing historical versions, it is useful to reduce the Search panel height once concepts are loaded for comparison, as shown in the adjacent screenshot.

Reloading clears Perspective: Comparing

Reloading the page will reset the SCT Browser to the Perspective: Full default presentation.

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| | With the same focus concept in each *Concept Details* panel, use their `History` context tab to change their content to a historical version, as described in [View the history of a SNOMED CT concept](/snomed-ct-user-guides/snomed-ct-browser-guide/how-to/view-the-history-of-a-snomed-ct-concept.md). |
| | The two *Concept Details* context tabs can now be used to independently select alternative versions from the concept history, so that they can be compared side-by-side. |
| | Once done with comparisons, select `Full` in the header bar `Perspective` button drop-down options list to switch back to `Perspective: Full`. |
| | The comparison focus concept will be retained in the `Perspective: Full` *Concept Details* panel, however, it will be reset to the latest published version. |
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