Ocular Head Up Display, Ocular Holoscreen, or simply HUD, is a Holographic Screen first used by Lt. Ryu Ketsueki, and the first version was developed by Ciel as a miniature version of her white retractile visor and adapted for only one eye, usually the right eye, as modification for one of Ketsueki's hearing aids, because the lieutenant couldn't always carry or hold a PADD with her, and the HUD is always connected to her PADD, to the Main Computer, and later the tricorder. The main use of the HUD is give notifications, status like Health and ammo. But it can also be used as aim for Type-3 Phasers and Long Range Phaser Rifles, show on-screen the data gathered by the tricorder like structure integrity.
Limitations
The HUD is only a display, and besides having its own independent system, it can be only interfaced through a PADD, a Console or a Tricorder. Without any PADD or Tricorder paired, the HUD is useless, and even the aim systems need to be paired with the Phaser or Rifle, something that can be done automatically once the user of the HUD holds the weapon. Same for the notification system, that needs to be paired with the user's PADD or the ship Main Computer.
Size
The Ocular Head Up Display Device, or simply HUDD, is very small, and can be installed in any Head Gadget such as a helmet, and can be used alone in a hearing aid or used two HUDDs together on Normal Glasses.