Sight Calc is a specialized calculator that eases the task of calculating sight reductions via the "Law of Cosines" method. It does not use Nautical Almanac data, so you must first compute LHA (Local Hour Angle) and declination, and determine your approximate latitude. It is designed particularly for students learning celestial navigation, such as the Celestial Navigation courses taught by the US Power Squadrons®. If you are unfamiliar with how to do sight reductions, some good resources are available from the U.S. Power Squadrons® at www.usps.org. In particular, this calculator is useful in conjunction with Form SR96a. Inputs are always
entered as two numbers: Degrees - left display, Minutes - right display.
If you already know the value in decimal degrees (e.g., 44.48833), key
it in followed by ENTER, then press ENTER again to indicate zero minutes.
Sight Calc will prompt you to enter six number in sequence: After you enter
each value, it will be displayed in decimal degrees in the corresponding
register. After you enter the last value (Dec minutes), Hc and Z will
be computed and displayed. ** In version 1.3 and later, enter North
Latitude as a positive number and South Latitude as a NEGATIVE number.
Sight Calc will take the absolute value of Latitude in the law of cosines
forumula, but needs the hemisphere to calculate azimuth (Zn). The sign
of Declination is positive if Latitude and Declination are the same
sense (both North or both South). If they are different, key the minus
sign before the first declination digit. If you want to do repeated
calculations with some of the same numbers, just enter the changed numbers
and press ENTER to accept the remembered values from the previous sight
reduction. To start over fresh at any time, press "C" to clear everything.
"CE" key clears the Current Entry. ## Example
The three numbers we need are LHA, DR Lat, and Dec. Starting with LHA degrees, enter each number in degree and minutes. Notice that after you type "338" and press enter, the prompt above the input registers changes to "Enter LHA (minutes)": Please report any bugs or suggestions to: sightcalc@nuvocom.com |
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