Methods and apparatus for a two chamber freezer whereby both chambers can be maintained at a substantially constant ultra-low temperature, such as within the range of about 40 C. The retention element includes a body mounted on a base, the base being slidable along a longitudinal guide rail. The output buffer further includes a pull-down circuit, including a first pull-down transistor for providing a first pull-down output signal and a supplemental pull-down circuit in parallel with the first pull-down transistor.