Clues Needed

[Bruce Plecan]

Being new to the scope world, and after reading a scope manual, I'm still at
a lose, and hope someone could clear these meanings up for me.
  When using the triggering mode selection there are these options.
Auto
+ Internal
- Internal
+External
-External
Auto-seems to mean that the pulses are displayed as they occur, and the
trigger
  sense lead need not be connected.
ALSO, for these 4 other options where would one hook the sense lead to.
Any help here appreciated.
Bruce
     Happy used to, really chase the skirts.
     But, having visited Scotland last weekend, has left him confused......