Ambush attacker is surprised?

[Peter V. Dell'Orto]

Originally Posted by The Benj

The "Surprise" rules are pretty clear on what happens when you're surprised and the difference between total and partial surprise, but are quiet on exactly HOW you achieve surprise.

I don't follow. If it's possible to have partial surprise, the rules seem pretty clear - it's a 1d roll, with modifiers as listed under Partial Surprise. I use this at least once a session, so I'm not seeing where it doesn't cover the "how."