An apparatus for determining a vertical level or density of a material column including a granular solid or a solid-liquid mixture, the apparatus comprising: a support member; and at least one measurement module; wherein the measurement module comprises: a support arm mounted to the support member and extending outwardly from the support member; a displacer (32a to 32e) mounted to the support arm; and a force measurement device configured to measure a force attributable to a mass of the displacer mediated by a buoyancy of the displacer (32a to 32e) in the material column, wherein the measurement module has a data connection to a data processing unit for transmitting measurement data from the measurement module to the data processing unit to generate level or density information about the material column, wherein the apparatus further comprises a vibration actuator configured to vibrate material surrounding the displacer (32a to 32e) in the material column to fluidize the material surrounding the displacer in the material column, characterized in that the displacer (32a to 32e) is mounted to the support arm via the force measurement device and the force measurement device is contained within the displacer. a support member; and at least one measurement module; wherein the measurement module comprises: a support arm mounted to the support member and extending outwardly from the support member; a displacer (32a to 32e) mounted to the support arm; and a force measurement device configured to measure a force attributable to a mass of the displacer mediated by a buoyancy of the displacer (32a to 32e) in the material column, wherein the measurement module has a data connection to a data processing unit for transmitting measurement data from the measurement module to the data processing unit to generate level or density information about the material column, wherein the apparatus further comprises a vibration actuator configured to vibrate material surrounding the displacer (32a to 32e) in the material column to fluidize the material surrounding the displacer in the material column, characterized in that the displacer (32a to 32e) is mounted to the support arm via the force measurement device and the force measurement device is contained within the displacer. a support arm mounted to the support member and extending outwardly from the support member; a displacer (32a to 32e) mounted to the support arm; and a force measurement device configured to measure a force attributable to a mass of the displacer mediated by a buoyancy of the displacer (32a to 32e) in the material column, wherein the measurement module has a data connection to a data processing unit for transmitting measurement data from the measurement module to the data processing unit to generate level or density information about the material column, wherein the apparatus further comprises a vibration actuator configured to vibrate material surrounding the displacer (32a to 32e) in the material column to fluidize the material surrounding the displacer in the material column, characterized in that the displacer (32a to 32e) is mounted to the support arm via the force measurement device and the force measurement device is contained within the displacer.