Set the values you want to apply, then click on Move, Scale or Rotate to transform all picked shells. If no shells are picked, all unlocked flattened shells are modified. If Local is ticked, the scales and rotates will pivot around the center of each individual shell, otherwise the origin (i.e. u=0, v=0) is used. Use the Invert button to invert all values so you can quickly transform shells back to where they were, and the Reset button resets the field values back to their defaults.

The three green buttons to the bottom left represent the left, middle and right mouse buttons. By default these are all on, indicating that you can rotate (left), translate (middle) and scale (right) shells by holding down the Space key. Click on any one of the green buttons to turn that function off. For example, if you don't want to accidentally scale any shells, click the third button so it turns gray.

Rescale U & V 

Use these buttons if you want to rescale shells so that their size in UV matches that in 3D. For example, if you load an OBJ with existing UVs and some shells are red and others are blue, clicking on the & button will rescale each of them up or down until they are closer to green in shading. Click on the U or V buttons if you only want to scale in that direction. As with the other transform buttons above, the rescale will only affect picked shells, or all unlocked shells if none are picked. [Example]

Normally UV shells in UVLayout are resized so that the texture scale is even across the entire surface; this is what the Rescale buttons above do. This means that when the checker texture is applied, all squares appear as close to the same size as possible.

Sometimes however you may want to assign increased or reduced scales to specific parts. Some examples would be increased scale of UVs in a creature's face and hands to get greater detail there, but reduced scale for the inside of the mouth where very little detail is required.

In previous versions of UVLayout it was possible to do this to a degree by simply scaling shells up and down, but they were rescaled back to their original size if any further flattening/optimizing was performed. It was also quite difficult to get a smooth transition between mixed scales within a single shell.

You you can now create and edit these mixed scale UVs using the following buttons. These replace the Green Balance tool which briefly appeared in UVLayout v1.19.3.  [Professional Version Only] 

Local 

When one or more shells are picked, all are locally scaled together so that, on average, they are closer to green; in this situation, individual shells may still show some red or blue shift, and these will be rescaled when optimized. When no shells are picked, all unlocked shells are individually processed and there will be no remaining red or blue shifts.

To use this tool, first use Scale above or Space-RMB to resize a shell (it will shift to red/blue as you scale it down/up), next Pick that shell with the LMB, then click on Local and it will shift back to green without changing size. If you then go to the 3D view and turn on the checker texture, you'll see that the squares in that part of the surface are a different size. If you re-flatten/optimize that shell, it won't change its size.

At any time you can see what local scaling has been applied by toggling the small white button to the right of Local. Blue shading indicates that those polys are scaled up, which will give you more detail in that area; red shading is scaled down, giving you less detail.

Smooth 

Shells with mixed scale UVs can be welded together and re-flattened, but at the junction between the two the UVs may be more distorted than usual because of the sudden change in scale. To fix this, click on the Smooth button; the local scaling will be averaged out across the junction, creating a more gentle transition after the shell is re-flattened.

Reset 

To remove any local scaling from picked shells, use Reset.