Gaidax is correct. Not sure if it is explained well. Wisdom bonus + Proficiency = perception modifiers. So they are showing you that you have a +2 and a +2 for a total of +4. But in all rolls, instead of adding those bonuses to your roll, they subtract them from the DC. Like lots of other things, the log needs a LOT of improvement. Many things are not shown, confusing or wrong. IMO this one is confusing and wrong, but the ending result is accurate.
