at773

User Manual
The latest User Manual can be found here:

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Frequenty Asked Questions
A good source for longitude and latitude is Bing Maps:
 * 1. How do I calculate longitude and latitude** (used to calculate sunrise and sunset)?

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 * //Example//**: The following address:

6845 W. Frye Road Chandler, AZ 85226

yields the folllowing results:

33.2980290055275 -111.961703449488 or: Latitude = +33.2980290055275 (positive indicates northern hemisphere (USA), negative indicates southern hemisphere) Longitude = -111.961703449488 (positive indicates eastern hemisphere, negative indicates western hemisphere (USA))

With rounding, enter: Latitude: 33N Longitude: 112W

Visit: [] to determine your time zone.
 * 2. How do I determine my GMT (Greenwich Mean Time)?**


 * //Example//**: For the Eastern Time Zone, enter -5.

Altitude is determined based on the measurement of atmospheric pressure. The greater the altitude, the lower the pressure. When a barometer is supplied with a nonlinear calibration so as to indicate altitude, the instrument is called a pressure altimeter or barometric altimeter. A pressure altimeter is the altimeter found in most aircraft. The calibration of an altimeter is of the form:   where c is a constant, T is the absolute temperature, P is the pressure at altitude z, and Po is the pressure at sea level. The constant c depends on the acceleration of gravity and the molar mass of the air. Here is an excellent guide provided by REI: [] Altimeters are often misunderstood because they do not measure your actual position on the earth (true altitude) such as a GPS, but measure the air pressure and predict the altitude based on this measurement.
 * 3. How does an altimeter work?**
 * 4. The altitude changes when I am not moving. Why does that occur?**

This is referred to as “Pressure Altitude”. Pressure Altitude is adversely affected by the true altitude and to a lesser extent, changes in the weather, often referred to as barometric pressure changes.

Thus, your Pressure Altitude can change without changing your position. These changes can be as great as a thousand feet (the changes due to weather are more pronounced at higher altitude).

To offset the difference between Pressure Altitude and True Altitude, you must calibrate the device at a known altitude, whenever convenient.

Visit: @http://www.csgnetwork.com/pressurealtcalc.html
 * 5.** Where can I find a good pressure altitude calculator?

To compare pressure conditions from one location to another, meteorologists correct pressure to sea-level conditions. Because the air pressure decreases as you rise in altitude, the sea-level corrected pressure (the pressure your location would be at if located at sea-level) is generally higher than your measured pressure.
 * 6. How do I calibrate sea-level pressure?**

Thus, your pressure may read 28.62 inHg (969 mb) at an altitude of 1000 feet (305 m), but the corrected pressure is 30.00 inHg (1016 mb).

The standard sea-level pressure is 29.92 in Hg (1013 mb). Pressure conditions greater than 29.92 inHg (1013 mb) are considered high pressure and less than are considered low pressure.

Most weather stations instruct you to find a reporting station near your location to identify the corrected pressure. A good source for calibration is:

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To be accurate, you must first calibrate your altimeter, than calibrate the sea-level pressure.

The temperature sensor is housed inside the unit and the entire unit must heat up or cool down to a steady-state condition. This is known as the //thermal mass time constant//. The unit must be placed in an open area, out of the sun and away from your body to recieve an accurate temperature. Unfortunately, the temperature sensor can not be exposed to the elements and must adjust based on the thermal mass of the unit.
 * 7. The temperature sensor is inaccurate or slow to respond. Why is that?**

The temperature sensor is required for altitude compensation and therefore, can be accessed to measure the ambient temperature, but is not nearly as responsive as a probe thermometer.

The forecast icon is a prediction based on rate of change of pressure, and requires some historical context to predict the weather conditions. Allow at least 72 hours for changes in pressure to take place. Please note that the forecast is only a prediction based on rising or falling pressure, and is considered an estimation 24-48 hours in advance, and is not accurate and is considered simply a tool to predict the weather. Also note that this is a prediction of future weather conditions and not a prediction of current weather conditions.
 * 8. The forecast icon does not appear to be accurate or it does not reflect current conditions.**

You must be fixed in one location for this function to accurately work. Once your altitude changes, the icon must be reset.

To determine high and low time, you must first set your longitude, latitude, GMT, date and time. Since high and low tides are greatly impacted by your location, you must also calibrate the lunitidal interval.
 * 9. Setting Tide.**

For more information on the definition of lunital interval, visit:

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Declination is the difference between true north and magnetic north (compasses measure magnetic north). To determine declination:
 * 10. Magnetic Declination.**

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