Abstract: An ink drop height sensing device for an ink jet recording apparatus, the apparatus including a nozzle for forming and propelling a stream of ink drops towards a recording media in a predetermined deflection plane. A light source on one side of the intended path or trajectory in the plane of deflection of the ink drops impinges upon a mask located on the opposite side of the plane, which mask is aligned with a light sensitive device such as a phototransistor located behind the mask. The mask includes first, second and third line sensors, in the illustrated instance serially arranged slots with at least two of the slots being in parallel relation, the third slot being inclined with respect to the parallel slots and positioned with respect to them so that at a predetermined point along its length, it is a predetermined distance from the next adjacent slot relative to the distance between the two parallel slots.