Perpendicular Snap Confusion

I have a general question regarding Autocad's Perpendicular Snap
behavior.
There are times when I am running Osnaps (with osmode set to 767) and
I click near a line or intersection and the Osnap goes to a
Perpendicular snap on the first click. This is different from the
tentative perpendicular snap that shows the .. next to the snap
symbol. This is the real snap point that starts the line at that
exact point. I am confused by this since I can't understand how you
can generate a perpendicular point with only one click. The
perpendicular point must be perpendicular to something so I would
think that you need at least two sources of input.
Does anyone have an explanation for this?

Zachary Kane

 

It's dangerous to run with the perps IMHO.

Specify version.

 

2000i
2005
I just got this to happon in 2005. By moving the mouse around a
dimension I got the Perpendicular snap to pop up on the end of my
slash mark. When I view the line it is actually a short distantance
off of the slash mark:

DIST Specify first point: Specify second point:
Distance = 0.00144113, Angle in XY Plane = 45.00000000, Angle from
XY Plane =
0.00000000
Delta X = 0.00101903, Delta Y = 0.00101903, Delta Z = 0.00000000

Where is the world did this point come from??


I do recogize that there is a danger with running with perpendicular
on as with nearest. There would be less danger if Autocad would only
use perpendicular on the second click!

Thanks
Zac.