The purpose of extension lines in a drawing is to?

The purpose of extension lines in a drawing is to indicate the starting point of a dimension. These lines are crucial in technical drawings because they visually connect the numerical measurement of a dimension to the specific feature or geometry being measured. By extending from the part to the dimension line, they clearly show where the measurement begins and ends, allowing anyone interpreting the drawing to understand precisely which parts are being referred to and how dimensions correspond to the actual physical features. This clarity is vital for ensuring accurate interpretation and manufacturing based on the drawing. Other options address different aspects of technical drawing but don't specifically pertain to the function of extension lines as effectively as this one does.