Start with eyeline and reading distance
Put the camera at the final height, sit or stand where the recording occurs, and measure from your eyes to the glass plane. Read a sample script at several type sizes. The best prompt size is not the biggest product: it is the smallest setup that keeps eye movement subtle, a useful number of words visible, and the speaker's posture natural at the intended framing.
Verify the complete camera path
Record the camera body, lens, filter thread, focal length, webcam dimensions, and any cage or adapter. Confirm a supported backplate, step-up ring, universal shroud, or phone mount, and make sure the lens centers behind the reflective area. Wide lenses are more likely to see glass edges, fabric, or internal reflections, so test the actual field of view.
Built-in display and tablet models trade different friction
An integrated display can act like another computer screen and keeps a dedicated prompt surface aligned, but it needs the specified USB bandwidth, software, operating system, and cable path. A tablet prompter can cost less and work independently, yet screen size, brightness, mirroring, remote control, device heat, and repeatable placement become the operator's responsibility.
Mount the total moving weight
Add the prompter, display, camera, lens, backplate, cables, and any light or microphone sharing the support. Compare that total with the arm or tripod rating and practical extension. A nominally strong arm can still bounce when typing on the desk or sag when the camera sits far from the pivot. Provide strain relief so USB movement does not shift framing.
Rehearse recovery, not only smooth scrolling
Test manual scrolling, hotkeys, remote controls, and any voice-follow feature with pauses, corrections, emphasis, and ad-libbed sentences. The speaker needs a fast way to stop, jump back, and resume without staring at controls. Record several minutes under normal key lighting to check readable contrast, reflected room objects, autofocus hunting, eye travel, and whether the glass changes image quality.