Print speed? Percent of what? -Ender 3 V3 SE-

When I set printing speed Tune -> Printing speed what percent is that?
Is it percent of current gcode phase, so 100% doesn't change speed or
Is it percent of normal (fastest) printing speed of used printer settings?

So when first layer is set to print slower speed does set to 100% makes it faster or not?

And is there any way to set for example 120% speed so it lasts whole time? Now when I set print speed it get overruled after next layer is started, so if I want to make it faster I have to sit next to a printer and gain speed after every layer is finished.