890B (HP)

From the atrium (section 2 achievement) go to the back of the room, up the stairs and turn right. Walk through the door on the right and into the calculus lab.
*note: i walked left, and triggered some dialogue about Luna's locked room, then 'my' room, and it mentioned the calculus lab at the other end of the hallway. Dunno if that causes it to show up or not but thats what i did, in case it doesnt work for you*

Section 1: 0:45
Section 2: 0:55
Section 3: 1:45
Section 4: 3:05
Section 5: 7:20
Section 6: 14:50
Section 7: 17:05
Section 8: 22:40
Section 9: 22:55
Section 10: 26:30

Achievement Walkthrough: