## Zero Dimensions and Signed Dimensions

All types of distance dimensions have a continuous domain of definition
that includes zero, negative and positive values. Fig. 1. shows a sketch
with a dimension that positions the geometry in both positive and
negative value domains. In the left image, the sketch dimension is
negative, and the image on the right shows the same sketch with
dimension sign changed from negative to positive.

```{figure} ../../pictures/S.2.3.1.png
:width: 15cm
:align: center

Fig. 1
```

Any type of distance and angular dimensions can have zero value. On the
same Fig. 28.3.1, a dashed line shows the geometry in a zero state, when
the dimension value is equal to zero.

Alternating signs are most typical for dimensions set for an object
oriented in space, for example, a line with a normal vectors. The line
divides space into two semi-planes, so the distance dimension between a
line and a point would have various signs depending on the side of the
line where the point is located. A point lying on a line would
correspond to zero dimension.

It is worth noting that the distance between the points is intrinsically
non-negative; but a distance dimension set for two points can be
negative or equal to zero. It has a practical sense when you work with a
parametric drawing. For example, the dimension with alternating signs
shown in the left and right sketch in Fig. 28.3.1, can be defined as
"distance from point to line" or "point-to-point distance" constraint.
In both cases, its behavior would be the same.