There are a total of three different horizon mirrors for our sextants:
Traditional split-view mirror:
It all started with the split-view mirror, which is why we also speak of a traditional split-view mirror. This mirror is fully mirrored on one half.
The full-view mirror is fully half-silvered and thus semi-transparent.
You can look halfway through the mirror in horizon direction and the other half of the viewing beam is mirrored in index direction.
The clear-view mirror was developed by Cassens & Plath. The central vertical part of the mirror is half-silvered and thus semi-transparent.
The sides are not mirrored and offer a clear view of the horizon.
The type of horizon mirror is partly already predefined in our sextant models, as e.g. a Schüler double prism cannot be used with a split-view mirror.