This is a quite recent feature in MARLIN firmware which regulates the pression applied to the extruder in order to allow faster and more accurate prints (specialy at the edges)

Looks very promizing as you can see on the picture :

• K = 0 ==> LIN_ADVANCE is disabled
• K = 75 ==> LIN_ADVANCE active
  both test cubes are printed at 60 mm/s including the external perimeters

I have not yet calibrated the best value for K, but the default setting for PLA seems already good.

everything is explained here (activation is inside configuration_adv.h)
http://marlinfw.org/docs/features/lin_advance.html

To install MARLIN in the ANET please follow short explanations in this thing

https://www.thingiverse.com/thing:2426747