Whats the red needle on the depth guage?

[silent one]

I know this sounds stupid but whats the red needle on the depth guage for . I can move it and it appears to spring back to where it is. It doesnt appear explained in the manual.

[shad43]

This appeared after the 1.2 patch, it seems to indicate periscope depth.
The one in the deeper gauge seems to indicate crush or maybe safe depth.

[DirtyHarry3033]

What shad43 said, on the "shallow" depth gauge it shows your periscope depth. On the "deep" depth gauge it shows your hull's test depth.