A data processing device (101) for processing telemetry data obtains sampled data based on output data from a plurality of sensors (103, 104, 105, 106) associated with a vehicle (102). The data processing device (101) generates first and second sets of sampled values using the sampled data. The first set of sampled values are associated with a first sampling time and the second set of sampled values are associated with a second, subsequent sampling time. The data processing device (101) derives a set of data elements, a data element being indicative of a measure of a change between a sampled value in the first set and a corresponding sampled value in the second set, a position of a given data element in the set of data elements having been determined based on at least one mapping rule. The data processing device (101) encodes the set of data elements and outputs data comprising at least the encoded set of data elements for transmission to a remote data processing unit (113).