A drum chopper in which cutting blades are locked in a form-fitting relationship to blade receptacles includes a locking structure between the blades and receptacles and a clamping piece. A control list identifies at least one feature in a mobile device. This combination creates a novel combination test technology capable of detecting a wide range of different analytes, and operating in a wide variety of wet or dry, in vivo or in vitro environments. Then, the matrix is partitioned into n columns of size Mq.