The – sign appears if the coordinate of the dimension is negative.
Generally, do not delete the – sign, but edit the dimension in the normal way.
Lines have an X-Y coordinate-system.
•The Origin of a Line is at its start-Point
•The +X-axis of a Line is from its start-Point(1) to its end-Point(2)
•The +Y-axis of a Line is at +90º from Line.
When we add a dimension that is a perpendicular-distance from the Line, the
•dimension will be Positive if in +y-axis half of the Line (blue area in the image)
•dimension will be Negative if in the -y-axis of the Line (green area in the image)
In the top image:
•Dimensions from the Line(1 to 2) to Points a and b will be positive
•Dimensions from the Line to Points c and d will be negative
The X-AXIS and Y-AXIS of a Part each has its own coordinate-system.
The image to the left shows the Coordinate-System of the Y-AXIS
The local +x-axis of the Y-AXIS of a Part is along the Y-AXIS!
Thus, the local +y-axis of the Y-axis of a Part is at +90º from Y-axis
Thus a dimension that is a perpendicular-distance from the Y-AXIS to a Point is in the green area will be negative ...
... and this is in the +X axis direction of the Part!