If you are not familiar with the concept of GD&T, we highly recommend to learn about it now. The example also makes clear that GD&T is essential to assure that parts fit well to assemblies.

The first point is 'classical' dimensioning while the 2 others are geometric information, thus GD&T comes into play. So just specifying the hole dimension and position is not sufficient.

The hole alignment is important because just drilling each hole at the given position without taking care of the axis, would lead to holes through which the axis will not fit. The straightness is important because a bent axis would not fit through the holes.

That the axis part must have a certain straightness.

That the holes are along a certain axis that is not perpendicular to the XZ base plane.The diameter of the holes and their positions.That means we have to specify the following things In the application an axis should be put through the 2 holes of the part. To achieve this, the system of Geometric Dimensioning and Tolerancing (GD&T) was developed. Since most parts have to fit to assemblies, also the geometric relations to other parts are important. The main purpose of a technical drawing is that others understand what the designer created with what tolerances AND how to manufacture the design.

Symbol for flatness on a drawing