Sight Calc is a specialized calculator for the iPhone or iPad 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 Off-Shore 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/eddept/jn/. In particular, this calculator is useful in conjunction with Form SR96a, www.usps.org/eddept/n/files/sr96a.pdf

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:
LHA (degrees)
LHA (minutes)
Lat (degrees)
Lat (minutes)
Dec (degrees)
Dec (minutes)
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.

Remember that Latitude is always entered as a positive number. 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.

Please report any bugs or suggestions to:

sightcalc@nuvocom.com