What is the measured value always positive from one point to another

It is called "distance". In fact, distance measures how far apart two points are from each other, and it is always a positive number.
In mathematics, for instance, the distance between two points of coordinates (x1,y1) and (x2,y2) on a xy-plane is defined as

and by definition, this number is always positive.

Energy stored in a spring
Work is done when a spring is extended or compressed . Elastic potential energy is stored in the spring. ...
The elastic potential energy stored can be calculated using the equation:
elastic potential energy = 0.5 × spring constant × (extension) 2