oh--you're asking about the "%" . Sorry, I thought you were asking about the range limits, which are thoroughly explained by the link.

The % is, I vaguely recall, some way of setting the percent of the predetermined range. It makes sense to the coders.

To avoid lag with other internet activities, I set at 85% of my tested upstream speed.

The slider display also doesn't react quickly to changes in the connection speed settings (old settings might be displayed, but when the slider is used, surprisingly change to the new range).