aquamedic triple doser

[bigblack]

hi wondering if anyone can help me, i bought this unit about 2 months ago but i find that it is not very accurate, could it be just this unit, i figured a dosing pump would be accurate to the ml but this one doesn't seem to be giving me the exact dose every pump its off + or - when i test it on the exact same time. How does it compare to the profilux or litermeter would those be the same or better. ??