Abstract: Measurements of pressure relative to atmospheric reference pressure are enabled by a sealed enclosure, which in one aspect is a variable volume enclosure including a movable element responsive to atmospheric pressure, to at least partially equalize pressure internal to the variable volume enclosure to the pressure external to the variable volume enclosure, such that a pressure sensor pneumatically connected to the internal volume can use its pressure a reference in measuring atmospheric pressure. The variable volume enclosure may house electronics and/or electrical terminations for pressure sensing, or the variable volume enclosure may be a sub-enclosure connected pneumatically to the pressure sensor, with another enclosure housing electronics or electrical terminations. In another embodiment, the sealed enclosure includes an absolute pressure sensor for sensing atmospheric pressure for use as a reference, and need not have variable volume.