Features of my interpretation of a portable electroinstallation level:

• Horizontal and vertical level
• 6 mm center rod for drill guiding
• 6 mm reinforced drill guides with distance marking
• 71 mm and 142 mm distance from center rod for 2 x and 3 x flush mounted boxes
• 91 mm distance from center rod for 2 x Single flush mounted boxes

Additional hardware needed:

• 15 x 15 x 40 mm levels (can easily be found on aliexpress)
• 6 mm rod (I used 45 mm aluminium rod due to availability)
• 8 mm pipe with 6 mm inner diameter
• Some kind of glue like superglue or epoxy

Printing:

• Nothing special required