to mark speed
I know,exactly.
I will tell you something I wanted to add to my previous post.
We were once hit by a lightning..we dropped and it all went dark for a bit.If it wasn't for the calm reaction and reassurance of the IN CHARGE CREW MEMBER on the day(who had experienced that before and knew exactly what was going on) I would have crumbled..it really was possibly the scarier thing that happened to me,and I will never forget lip reading his words.."It's a lightning"..
PS:I thought we had hit another aircraft..silly me!!
it was all foggy and dark..