An ink jet printer or a print head for an ink jet printer, the printer or print head having a printing position from which ink can be ejected for printing and the printer or print head being suitable for mounting alongside a conveyor so that the conveyor can convey products, to be printed onto, past the printing position of the printer or print head in a conveying direction, the printer or print head comprising: a first sensor (77a, 77b), for sensing the presence of a product passing the first sensor, and a ramp portion extending away from the printing position, the ramp portion being suitable to be mounted in a manner, when the printer or print head is mounted alongside a conveyor, so that it extends upstream, relative to the conveying direction, of the printing position and so that it has a ramp surface facing the conveyor, the ramp surface being angled relative to the conveying direction with the end of the ramp surface that is furthest from the printing position being further sideways from the conveyor than the printing position, characterised in that (a) the ramp portion is such that when it is mounted in the said manner, a place on the ramp surface spaced from the end is no further sideways from the conveyor than the printing position, whereby a product conveyed by the conveyor that strikes the ramp surface between its end and the said place will be forced sideways relative to the conveying direction as it is conveyed past the ramp surface so as to be no further sideways than the printing position before it reaches the printing position; (b) the first sensor is mounted on the said ramp portion; and (c) the printer or print head comprises a second sensor (79a, 79b), for sensing the presence of a product passing the second sensor, the second sensor being spaced from the first sensor in the direction from the first sensor towards the printing position. a first sensor (77a, 77b), for sensing the presence of a product passing the first sensor, and a ramp portion extending away from the printing position, the ramp portion being suitable to be mounted in a manner, when the printer or print head is mounted alongside a conveyor, so that it extends upstream, relative to the conveying direction, of the printing position and so that it has a ramp surface facing the conveyor, the ramp surface being angled relative to the conveying direction with the end of the ramp surface that is furthest from the printing position being further sideways from the conveyor than the printing position, characterised in that (a) the ramp portion is such that when it is mounted in the said manner, a place on the ramp surface spaced from the end is no further sideways from the conveyor than the printing position, whereby a product conveyed by the conveyor that strikes the ramp surface between its end and the said place will be forced sideways relative to the conveying direction as it is conveyed past the ramp surface so as to be no further sideways than the printing position before it reaches the printing position; (b) the first sensor is mounted on the said ramp portion; and (c) the printer or print head comprises a second sensor (79a, 79b), for sensing the presence of a product passing the second sensor, the second sensor being spaced from the first sensor in the direction from the first sensor towards the printing position. (a) the ramp portion is such that when it is mounted in the said manner, a place on the ramp surface spaced from the end is no further sideways from the conveyor than the printing position, whereby a product conveyed by the conveyor that strikes the ramp surface between its end and the said place will be forced sideways relative to the conveying direction as it is conveyed past the ramp surface so as to be no further sideways than the printing position before it reaches the printing position; (b) the first sensor is mounted on the said ramp portion; and (c) the printer or print head comprises a second sensor (79a, 79b), for sensing the presence of a product passing the second sensor, the second sensor being spaced from the first sensor in the direction from the first sensor towards the printing position.