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Sight Calc

By Nuvocom Incorporated

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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 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:
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:

What's New in Version 1.1

Launch image for 4" retina displays.

iPhone Screenshot

iPhone Screenshot 1

Customer Reviews

Sweet App ... But the Azimuth Can Be Wrong

I love this App! It looks like it has been out for a while and had a lot of good reviews. I'm only putting this as a 2-star review at this time to bring attention to the fact that using this App when you are lost at sea may get you lost even further!

From my testing the result Hc and Z is spot on! But will the sailors using an app like this know the difference between Z and Zn? If you assume that the result Z value is your azimuth and graph your sight based on that value, you are going to be lost at sea. Another correction is required to determine the azimuth. You have all of the inputs to make this correction, why not provide the azimuth output?

As documented in the Ho229 tables:

Latitude SAME Name As Declination - N. Lat, LHA < 180 .... Zn (azimuth) = 360-Z
Latitude CONTRARY Name to Declination - S. Lat, LHA < 180 .... Zn (azimuth) = 180+Z

The app is very easy to use and does the basic calculations correctly. Please calculate and output the azimuth and I will gladly update this to a 5 star review!

Well pleased

As a USPS sight folder reviewer, your app has saved me hours of laborious effort. Thank very much for taking the time to make this job easier. The app works perfectly.

works well

Simple, straightforward, works well. I use it to check sight reductions done with HO 249; it’s comforting to have an app give the same result as table lookups. Thanks.

Sight Calc
View in iTunes
  • Free
  • Category: Navigation
  • Updated:
  • Version: 1.1
  • Size: 1.1 MB
  • Language: English
  • Seller:

Compatibility: Requires iOS 5.0 or later. Compatible with iPhone, iPad, and iPod touch.

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