A precision apparatus has a movable member (A), moving in a bridge element (2) arranged perpendicular to the movement of the moveable element. The bridge element comprising an air slit (S) and a exhaust (E). The bridge element (2) comprises a primary air duct (21), substantially extending along the length of the bridge element, which primary air duct is provided with apertures (21a, 21b), The apertures (21a, 21b) are evenly distributed along the length of the bridge element, and form an air flow passage to a secondary air duct (22), also substantially extending along the length of the bridge element Through the secondary air duct in operation air is drawn through the air slit (S).