The – sign appears if the coordinate of a 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 0,0 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 you add a dimension that is a perpendicular-distance from the Line, the:
•dimension is Positive if in +y-axis half of the Line (blue area in the image)
•dimension is 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 are positive
•Dimensions from the Line to Points c and d are negative
The X & Y-axes of a Part also have their own coordinate-system.
The bottom 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!
In the bottom image:
A dimension from the from Y-axis to Point (a or b) in the Blue area is Positive.
A dimension from the Y-axis to a Point (c or d) in the Green area is negative.