Scale
This tool scales the selected UV components uniformly about the UV coordinate closest to the pointer, which is represented by a cross.
If you have selected a single UV point instead of a polygon, you will be unable to scale since UV points have no spatial dimensions. You can only scale if at least two UV points are selected, in which case they will be scaled from their common center.
Scaling a grid of 5x5 points, showing the small black cross which represents the common center.
Double-click on UV Points
You can double-click on UV points with the Move, Scale and Rotate tools and the following dialog window will open:
The point on which you clicked can then be repositioned numerically in UV space.
Active Tool manager options
The same options apply as for the Move tool.