Measuring shoulder angles:
The ideal slope of the shoulder is 45 degrees. To measure slope of the shoulder you must measure the angle of the scapula in relation to the horizon. The slope of the shoulder is always measured against the horizon.
To measure, start at the point of the wither (bisecting the scapula, not above or below the scapula) and measure to the point of shoulder. Next measure from point of shoulder to point of elbow. Your horizon line should begin at the point of the two lines.