General
The unit name names are stored in a YAML file located in avalon/config/controlled_vocabulary.yml. The controlled vocabulary file has key/value pairs that store. This file is loaded every time it is needed and is never cached. Therefore, the file can be changed without restarting Avalon.
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The purpose of the unit vocabulary is to ensure that collections are saved with a proper unit. Changing or removing unit names in the controlled vocabulary file will not update or remove those unit names from collections.
Ordering
Unit vocabulary names are shown in the interface based on their insertion order in the controlled vocabulary file. The first entry in the file is also the first entry that will be shown when the units are listed in the Avalon interface.