Marine Barometer is a barometer sensor interface that is uniquely designed to meet the needs of mariners who rely on accurate atmospheric pressure for weather routing and the evaluation of weather maps. Pressure readings can be manually saved permanently along with the latitude, longitude, and time of the reading. If a sensor offset has been applied, that value is also stored with each recorded pressure. These recorded pressures can then at the navigator's convenience be transferred to the vessel's printed logbook. The GPS sensor is accessed for latitude and longitude only. The elevation of the sensor (your iOS device that includes a barometer) above sea level must be entered manually. Elevation values from the GPS are not accurate enough for the intended application. The concept of sea level pressure is explained along with how it is determined from the sensor reading. Instructions are provided on how to check the calibration of the sensor, and a sensor offset can be applied as needed. Links to sources of accurate sea level pressure are included. Sources of accurate elevation are included for use on land. The standard units for marine applications are millibars (mb) or hectoPascals (hPa). The main pressure display can also be set to inches of mercury, millimeters of mercury, or kiloPascals. However, because the primary reference pressures that would be used to check the sensor calibration are in mb, the sensor calibration must be set using millibar units. Reference links are provided for learning more about the tactical use of pressure for weather forecasting and weather map evaluation. Discounts are offered for barometer related reference books.