1. Lidda is sneaking through the woods. She spots a lone orc guard leaning against a tree in a clearing. Lidda decides to creep up behind the orc and stab him in the back. This is a Move Silently check, right?
1. Maximum visiblity in light woods is 3d6 x10 feet. Let's call it 100 feet.
2. GM has determined that Lidda sees Orc, but Orc has not seen Lidda.
3. How far apart are Lidda and the Orc at the start of the encounter? Roll a Spot check for Lidda to determine this, per the encounter rule: d20 + Spot skill x 10 feet. But, this total cannot exceed line-of-sight of 100 feet (so, we consider any total of 11+ as a total of 10, starting the encounter at maximum visible range. A roll of 8 means the encounter starts at 80 feet. A roll of 14 means that encounter starts at LOS, which is 100 feet. We roll and get a total of 5, which means Lidda saw the Orc at 50 feet away.
3a. If the GM knows how far the orc is from Lidda, then apply a -1 penalty per 10 foot to the throw. If the GM doesn't know, then use the above method.
4. The orc has his back to Lidda, so he will need to use his Listen check in order to catch her sneaking up on him. Since the orc is looking elsewhere, the -5 distraction penalty applies. Lidda starts the encounter 50 feet away, so the first Listen check is made at a -5 distance penalty. If the orc's Listen skill gives him a +1 modifier, then his passive Listen is (Taking 10) 10 + 1 Skill - 5 Distraction - 5 Distance + 2 undergrowth, for a DC 3.
4a. Lidda's Speed is 30. This is halved for harsh terrain. This is halved again to avoid movement penalties to her Move Silenlty check. She can move 7 feet per round. Let's adjust this to 10 feet per round for easy figuring. She needs to cross 50 feet. So, this will take her 5 rounds.
Lidda's Move Silently: d20 + 6 skill
Check 1: 50-40 feet. Move Silently vs. DC 3.
Check 2: 40-30 feet. Move Silently vs. DC 4.
Check 3: 30-20 feet. Move Silently vs. DC 5.
Check 4: 20-10 feet. Move Silently vs. DC 6.
Check 5: 10-5 feet. Move silently vs. DC 7.
This means that Lidda can automatically sneak up on the orc.