The CTD unit weighs about 1000 lb. and is lowered via cable to depths of 500m (1600 ft). Along the descent and ascent, the unit measures salinity, temperature, depth and chlorophyll levels. These readings are sent through the cable back to one of the ship's onboard computers where the data is monitored. On the computer screen, each of the environmental factors is depicted by a different color line which traces the levels for the various depths. From the computer, the CTD's bottles can be closed on command to collect sea water at various depths.