Abstract: According to examples, an apparatus may include a first pressure sensor to measure a first pressure level at a first height within a particulate material contained in a container and a second pressure sensor to measure a second pressure level at a second height within the container, in which a gas is to be supplied into the particulate material at a predefined velocity, wherein the first pressure sensor is to measure the first pressure level and the second pressure sensor is to measure the second pressure level while the gas is supplied into the particulate material at the predefined velocity. The apparatus may also include a controller that may determine a pressure gradient from the first pressure level and the second pressure level and calculate a height of the particulate material in the container from the determined pressure gradient.

Abstract: According to examples, a processor of an apparatus may access a plurality of measurement values corresponding to build material particles reclaimed from a build chamber during a period of time in which a reclamation operation is performed. The plurality of measurement values may be determined at a first hopper of the reclaimed build material particles as the build material particles are reclaimed from the build chamber and received into the first hopper. The processor may also calculate variances among the plurality of measurement values, determine whether a calculated variance of the calculated variances falls below a predetermined threshold value, and based on a determination that the calculated variance falls below the predetermined threshold value, stop the reclamation operation.

Abstract: An example of an apparatus is provided. The apparatus includes a vacuum source to draw gas and a build material from a build process. The apparatus includes a filter to separate the build material from the gas. A filtered portion of the build material is to be deposited on the filter and a collected portion of the build material is to be redirected. The apparatus includes a storage container to receive the collected portion of the build material. The apparatus includes a mass estimation engine to determine a total mass of the build material. The mass estimation engine is to estimate a mass of the filtered portion.

Abstract: According to one example, there is provided an apparatus comprising a supply station to receive a container, and a controller to determine when a build material container is present in the supply station and to cause the supply station to rotate the build material container to transfer build material between the build material container and a build material store, and determine when a post-processing container is inserted into the supply station and to cause the post-processing container to rotate to perform a post-processing operation on a three-dimensionally printed object in the post-processing container.