Droplet deposition apparatus comprises a base and a printhead adjustably mounted on the base and positionable relative to a datum on the base such that a swath of print produced by the printhead is in a predetermined position relative to the datum, the base being locatable on a printer using the datum. In one preferred form Nitinol alloy particles are used for the SMA particles. A receiver detects the variable applied by the drivers and changes in the variable in the field surrounding the object in the sensor-active region. The example method may also include storing performance data describing a performance indicator of the search.