From which direction does AutoCAD start measuring angles?

Measurement starts from3. Upwards is +Angle. Downwards is -Ve Angle. Below picture shall make everything very simple.

3 o clock 0 degree and 12 o clock 90 degree

start  +Angle 

downwards is - ve

ACAD can start from any direction for starts measuring an angles (O clock , Counter o clock ) from left to right and vise verse . 

3 o'clock

In AutoCAD By default, positive X, (3 o'clock) is0 degrees, Positive Y, (12 o'clock) is90, straight across negative X (9 o'clock) is180, etc..

Please read this Artical.

The Observation Editor section contains a graphical representation of the inside of the inspected section looking from the ‘from manhole’ toward the ‘to manhole’. The observation editor is further delineated by twelve wedges representing positions on a clock.

Observations in the observation editor are depicted as follows:

Observation Editor

• A point on the dashed line indicates a point damage observation. For example, a point placed at the6-o-clock position means damage is localized to that specific point in the section.
• A solid line running around the dashed line indicates a lateral damage observation. For example, a solid line running along the dashed line from7-o-clock to10-o-clock means damage running around the circumference of the section between the7- and10-o-clock positions.
• A point with an arrow pointing toward or away from the center indicates alongitudinal damage observation. For example, a point at5-o-clock with an arrow pointing toward the center means there is damage along the length of the section starting at the5-o-clock position and running for a specified distance.
• A dashed line running around the dashed line indicates a combination of a lateral and longitudinal damage observation with a beginning at one clock position and an end at another clock position. For example, a dashed line running along the dashed line from12-o-clock to3-o-clock means there is damage starting at the12-o-clock position and ending some distance along the section at the3-o-clock position.