Hasselblad focus screen red tab

[kahlheins]

Can anyone tell me why some Hasselblad focussing screens have a little red tab on the bottom face? I got intrigued when I saw this and couldn't find any information online

 

[Sirius Glass]

I am guessing it means "This side down".

 

[kahlheins]

I am guessing it means "This side down".

Is it that simple? I have only seen this on very few screens, but always thought it had a deeper meaning.

 

[itsdoable]

We used it as an orientation mark. Place it at the bottom, and the screen was always in the same orientation. Sometime useful for debugging out of focus corners.