To add a HUD to a level:
1) Install any entity.
2) Set properties:
- Always active on yes
- Static Mode to no
3) In the Main property, specify the script "stv233 / stv233_hhud.lua"
4) In the Name property, specify the number that will be considered 100% health. (If the figure is not specified, the amount of health that the player had at the start of the level will be considered 100%)
You can turn off the display of some elements by looking inside the script and finding the settings section.