As a machinist,you will need to measure acute angles,right angles, and obtuse angles (Figure C-233). Acute angles are less than 90 degrees. Obtuse angles are more than 90 degrees but less than 180 degrees. Ninety-degree or right angles are generally measured with squares. However, the amount of angular deviation from perpendicularity may have to be determined. This requires that an angular measuring instrument be used. Straight angles, or those of 180 degrees,and generally fall into the category of straightness or flatness and are measured by other types of instruments.