xe dan

ive not long brought my second impreza the car is a uk 2000 model it has a few mods one of them is a apexi fc command unit ive got the hand set showing boost, water temp,timing,ect it also shows knock sensor now should this read anything ? as now and then it moves very slightly is this anything to worry about? also is the knock sensor picking up an actual knock or does it pic up deternation as i wasnt sure ? the car runs fine without fault i just wondered if it was worth worrying about cheers