Abstract: Device (10) for guiding a user to mark a core sample (12) carried by a core tube (14), the device (10) including: a housing (20) mountable relative to the core sample (12) or the core tube (14) and having a marking guide (22) configured to be arranged adjacent the core sample (12) to guide marking; a communications module (26) operable to communicate with the downhole tool (16) to receive data; a user interface (28) operable to convey perceptible feedback to the user; and a processor (30) and associated memory (32). The processor (30) is configured to store data in the memory (32) and determine a marking position based on the data, and operate the user interface (28) to direct the user to cause relative rotation of the marking guide (22) and the core sample (12) so that the marking guide (22) is aligned with the marking position, allowing the user to use the marking guide (22) to mark the core sample (12) at the marking position.