This form is accessed from the Tidy Autosize Text tool.
Auto Scale Text
Impact calculates the extents of the current layer, and uses the smaller value of the x and y extents when calculating the scale. The text width will be the layer extents divided by the given scale. So, you can enter a new scale and the width will be recalculated or you can enter a new width and the scale will be recalculated accordingly.
Scale
Enter the required scale. The width will be updated automatically.
Width
Enter the required width. The scale will be updated automatically.
Text
Check this option if you want to selected text entities to have their width changed.
Dimensions
Check this option if you want to selected dimension entities to have their width changed.
You can press the Apply button to see the result of the chosen scale factor or width without closing the form.