A question via email drew my attention to the fact that the docs of Neptune (https://doc-snapshots.qt.io/neptune3ui/neptune3ui-overview.html#instrument-cluster) do not tell the user how to control (change values) of tell-tales. In the current implementation, they can be controlled only from the Dev section of the Companion app and be driven by the simulation. Currently, this is not mentioned anywhere, plus, a user cannot see telltales being controlled (showing up on the screen) any time since they are not a part of the simulation either. Before changing/extending simulation, a first step could be just to mention that the Companion app can be used to control telltales.
On this way, I additionally suggest to mention that Cluster automatically starts a simulation (a new feature in Qt IVI) which is written in QML and can be changed.