Use a nixie clock as app widget for the Home screen. You can resize it as wel as set unlimited amount of app widgets.

Use a light bulb clock in full screen mode with option keep screen on.

Use settings of appearence and create unique digital clock looks like digital clock on vacuum gas indicators.

* Select color of digits, background, grid, glow;
* Set visibility of seconds, AM/PM, glow, grid;
* Select appearence of bulb.

App supports all screen resolution without lost of quality.

Stability of the clock is guaranteed without additional permissions and global settings.