There are probably many different ways, depending on the accuracy required. Why not copy the angled line for every upward stroke, place the copies and simply adjust the length? Join with downstrokes.
Rotate everything so that the angled stroke is vertical or at 45 degrees, draw the graph holding shift at the appropriate times and then rotate back to the desired angle.
Convert the stroke to a guide ...and copy.
Extreme Path Plugin will do it!
You may create a long version (longer than the longest relevant segment) of the Guideline above the Path in the stacking order, and for each Segment, with View>Smart Guides on (snap messages shown below):
1) With the (normal) Selection Tool (toggle to it with V) select the leftmost Anchor Point of the Guideline line and snap it to the leftmost Anchor Point of the segment (Anchor);
2a) For same angle and length: With the Direct Selection Tool (toggle to it with A) Drag (to move freely) snap the rightmost Anchor Point of the segment to the rightmost Anchor Point of the Guideline (Intersect);
2b) For same same angle and unchanged width of segments/path: With the Direct Selection Tool (toggle to it with A) ShiftDrag (to move vertically) snap the rightmost Anchor Point of the segment to the Guideline (Intersect);
Presuming you wish to keep the other segments of the Path unchanged:
3) DirectSelect the remaining Anchor Points of the Path (just drag over everything and deselect the rightmost Anchor Point of the Guideline) and Object>Transform>Move; just use the vertical value already there, identical to the move in 2).
This should be accurate.
No need for pathGuides, temporary paths, etc. Assuming from your description you want the selected anchor to be positioned 45 degrees from both its adjacent anchors, it can be done in one move (at least in AI10 through CS3). See online Help. Read about SmartGuides and experiment until you are completely comfortable with the feature. It's one of the most important features in Illustrator.
Shown is CS3. SmartGuides has been modified in CS4, so again: To learn how to use Illustrator, read the instructions!