A positioning apparatus including a quill on which a probe apparatus can be mounted, at least one motor for positioning the quill in a substantially vertical dimension, and a pneumatic counterbalance mechanism for the quill. The positioning apparatus is configured, based on at least one factor relating to the quill, to automatically effect a change in the pneumatic counterbalance mechanism's pressure so as to thereby adapt the counterbalance force on the quill provided by the pneumatic counterbalance mechanism.