The edit fields indicate (from left to right) the lower limit,
the current value, and the upper limit. You can change the gain in two ways:
by manipulating the slider, or by entering a new value in the current value field.
You can change the range of gain values by changing the lower and upper limits.
Close the dialog box by clicking the Close button.

If you click the left or right arrow of the slider, the current value changes
by about 1% of the slider range. If you click the rectangular area to either
side of the slider's indicator, the current value changes by about 10% of the slider range.

To apply a vector or matrix gain to the block input, consider using the Gain block.