The Amount panel contains a Horizontally and Vertically box for the Scale Horizontal /Vertical action:

The Scale Horizontal action will only show the Horizontally box, while the Scale Vertical action will only show the Vertically box.

You can type directly into the boxes. Use the spin buttons to increase or decrease the percentage. Alternatively, use the slider underneath the box to increase or decrease the number.

Note: The red colour indicates negative numbers while blue indicates positive numbers.