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A huge time saver for anyone taking one of the US Power Squadron off-shore navigation courses.

Sight Calc is a specialized calculator for the 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. 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.

**NEW in version 1.3: 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 formula, but needs the hemisphere to calculate 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 clears just the Current Entry.

Please report any bugs or suggestions to:


What’s New

Version 1.5

Adjusted flipside command bar for iPhone X.

Ratings and Reviews

5.0 out of 5
6 Ratings

6 Ratings

PeterB26 ,

Quick Basic Sight Reduction

You put in the LHA, plus the AP Lat or DR Lat, and the declination, and out pops azimuth, true azimuth, and Hc. Couldn’t be easier to learn and use and is a great time saver.

You can also input a meridian angle eastward instead of the LHA by inputting it as a negative LHA. I find that calculating a meridian angle eastward is more intuitive for rising bodies than LHA so this saves me the step of converting it into a LHA.

If you understand how celestial works it will also give you great circle initial course and distances just as easily. Just substitue the difference in longitude for the LHA and the Lat of your arrival for dec.

I have not yet tried using it to pre-calculate altitudes for planning sights but I’m sure it would be handy for that too.

Five stars for simple easy and very useful!

jjmmss01 ,

Good for USPS Navigation and Jr Navigation Courses.

I used this a lot to get through my Jr Navigation course last year with The United States Power Squadron. It was a tremendous work saver.

TridentMiami ,

Sight Calc-Don't Take JN Without It !!

Slide rules and scientific calculators are not my thing. Many thanks to sight Calc for getting me through the USPS JN course!

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  • Family Sharing

    With Family Sharing set up, up to six family members can use this app.

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