Which statement correctly distinguishes flatness from straightness?

Which statement correctly distinguishes flatness from straightness?

• A. Flatness controls deviation of a surface from a plane; straightness controls the deviation of a line from a straight line.
• B. Flatness controls deviation of a line; straightness controls deviation of a plane.
• C. Flatness applies to edges only; straightness applies to faces.
• D. Flatness and straightness are interchangeable.

Answer: (A)

In geometric tolerancing, flatness and straightness describe two different ways a feature can deviate from ideal geometry. Flatness measures how far every point on a surface can stray from an ideal plane, by defining a zone between two parallel planes that the entire surface must fit into. Straightness measures how far a line or axis can deviate from a perfect straight line along its length, restricting the line to stay within a narrow band around that straight path. So the correct idea is that flatness controls the deviation of a surface from a plane, while straightness controls the deviation of a line from a straight line.

In geometric tolerancing, flatness and straightness describe two different ways a feature can deviate from ideal geometry. Flatness measures how far every point on a surface can stray from an ideal plane, by defining a zone between two parallel planes that the entire surface must fit into. Straightness measures how far a line or axis can deviate from a perfect straight line along its length, restricting the line to stay within a narrow band around that straight path. So the correct idea is that flatness controls the deviation of a surface from a plane, while straightness controls the deviation of a line from a straight line.