Profile: Nielsen-Kellerman Company designs, manufactures and distributes waterproof instruments. Our products include hand-held weather devices, soaring instruments, wind meters and weather trackers. Our Kestrel® 4000 pocket wind meter unit has a night-vision preserving back-light which helps users to sustain natural night vision. It incorporates an optical filter to reduce overall brightness & minimize blue and green spectrum light to preserve night vision. Our Kestrel® 3500 Delta T incorporates barometric pressure correction in its wet bulb temperature calculation, ensuring accuracy even on low pressure days, at high altitudes, and in very dry weather when Delta T monitoring is important.