This diver‐portable instrument measures relative depths to a precision of ±0.02 m in real time by using two sensitive pressure sensors. It fulfills a need by diver scientists to measure relative water depths in any underwater current in which diving is possible, but without being encumbered by unwieldy equipment such as was used previously. Typical applications include the measurement of stratigraphic levels on sea‐bed sites of historical, biological, and geological interest.