The current GATT characteristic list mentions it was up to date as of populated 2015-09-28. In the last 6 years, significantly more characteristics have been added to the Bluetooth spec. While it's not necessary to have all these constants available in Gadgetbridge, it's useful while implementing new features for a device or adding support for a new device
This was retrieved from https://btprodspecificationrefs.blob.core.windows.net/assigned-values/16-bit%20UUID%20Numbers%20Document.pdf. The GATT characteristics were parsed from that PDF and converted to constants with names via:
```
String description = uuid.description.trim().toUpperCase().replace(' ', '_').replace('-', '_');
System.out.println("public static final UUID UUID_CHARACTERISTIC_" + description + " = UUID.fromString((String.format(AbstractBTLEDeviceSupport.BASE_UUID, \"" + uuid.uuid + "\")));");
```
