Using a Handheld Instrument
Handheld battery-powered instruments are routinely used to obtain weather observations and will be the most likely tool available to you when you are ship-board. These instruments typically contain electric meters as well as a means of measuring temperature. Take the observation at a location out of direct sunlight and with the instrument held away from your body temperature or other heat sources. You will need to allow time for the instrument to adjust to the ambient conditions. If temperatures are very warm or very cold, it could take the instrument a couple minutes to adjust.
AG2 Ferguson offers some pointers for correctly using the handheld instrument.
AG2 Ferguson: "Hand-held meteorological instruments are an easy option for measuring temperature and pressure. To utilize this instrument, you want to stand in a cool, shaded area of the ship that closely resembles the ambient temperature around the ship. You need to stay away from external heat sources, such as smokestacks. The device measures ambient temperature, wet-bulb temperature and dewpoint temperature. Once these have stabilized, you can use the storage button to record at a later date. It also measures barometric pressure, pressure altitude, and density altitude. Once these have stabilized, you can also store these for use at a later time."