I've no idea, but does it matter? The unit is marked "TOP", so I always have put it this way up, although I found out by accidentally moving one on one of my cars about 30+ years ago. I was getting funny readings (can't remember what) from my temperature and fuel gauges. What's common I asked myself. Temp gauge and fuel gauge both are fed from the 10volt supply from the stabiliser. So I looked up one of my manuals and it mentioned fitting the stabiliser with "TOP" to the top. Checked it out, found I'd accidentally twisted it, levelled it, problem went away, never to return.

Moral: the manufacturer who made the devise knows more about it than me, so follow his instructions!

Nick Welch