Actually, @keithb775406 is correct. NH is Nautical Height, just as FE is Field Elevation.
“Nautical” is not a reference to units. It is a reference to the sea. Mean Sea Level Pressure is a bit of a mouthful. Not sure who or when but somewhere along the way, altitude above sea level, became nautical height.
To add to the confusion, altitude, height and elevation are interchanged throughout the currently used terms. Internationally we cannot seem to agree on a standard measure for anything. There are more ways to measure most things than anyone can possibly hope to learn.
To answer @PristineInk5669 , there is no one, correct answer here. In North America we still use inHG (Inches of Mercury) to measure barometric pressure. As @Nijntje91 said, MB (millibars) is pretty much exclusive to UK while most of the remainder of the world uses hPa (hectopascals).
If the region you are flying is using MB or hPa then they should refer to the altimeter setting as QNH, while if using inHG they should be saying Altimeter Setting. Most NA aviation authorities are pretty lazy though. I seldom here anything other that, “Current altimeter 30.01”. Some even drop “Current”.
Try building something, while farming part production to multiple international companies. Everyone has there own machining/engineering units. Conversions are usually rounded. Good luck when you get all the pieces.
Who knew that a rope is .164 meters? I thought you could cut it any length you wanted.