Sight Calc 4+


Designed for iPad

    • 5.0 • 6 Ratings
    • $1.99



Speed through the tedious and error-prone calculations of your Celestial Navigation course with Sight Calc v.2.0! Approved for use in U.S. Power Squadrons® courses.

Sight Calc is a specialized calculator for 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 United States Power Squadrons®. If you are unfamiliar with how to do sight reductions, some good resources are available from the United States Power Squadrons® at In particular, this calculator is useful in conjunction with Form SR96a,

Inputs may be entered as two numbers:
Degrees - left column
Minutes - right column
Or enter as decimal degrees (e.g., 44.48833).

Sight Calc will prompt you to enter six number in sequence:
LHA (degrees)
LHA (minutes)
Lat (degrees)
Lat (minutes)
Dec (degrees)
Dec (minutes)

In v 2.0 you may enter values in any sequence. Hc, Z and Zn are continuously computed and displayed.

Be sure to 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 azimuth (Zn). Similarly, enter Declination as positive if North and negative if South. (Note: this differs from version 1.x of Sight Calc.)

If you want to do repeated calculations with some of the same numbers, just enter the changed numbers.

To start over fresh at any time, press "C" to clear everything. "CE" key clears the Current Entry. Optionally, use the "o" key to convert minutes to decimal degrees, add that to the degrees field, and clear the minutes field. This has no effect on the calculation.

Please report any bugs or suggestions to:

What’s New

Version 2.0

• Simpler, more flexible user interface
• Fields can be entered in any sequence
• Declination entered as negative if South, positive if North
• New ° key converts minutes to degrees
• Minus key flips the sign of degrees fields
• Approved for use in United States Power Squadrons® courses
• v 2.0 is a complete rewrite in SwiftUI
• Supports Dark Mode

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!

App Privacy

The developer, NUVOCOM INCORPORATED, indicated that the app’s privacy practices may include handling of data as described below. For more information, see the developer’s privacy policy.

Data Not Collected

The developer does not collect any data from this app.

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  • Family Sharing

    Up to six family members can use this app with Family Sharing enabled.

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