Does any one know how the horizontal retrace (trigger) works on an
oscilloscope?  If you just use level triggering then how can you stabilize a
digital signal like this one:

      ____     ____              ____     ____
     |    |   |    |            |    |   |    |
     |    |   |    |            |    |   |    |
_____|    |___|    |____________|    |___|    |________


sometimes it would trigger off of the first pulse and sometimes of off the
second.  This would cause the wave to jump around.  I have used an analog
scope were this signal is rock solid.  How does it work?

Zach