# Sight Calc > Celestial navigation sight reduction calculator using Law of Cosines. (iPhone/iPad app by NUVOCOM INCORPORATED.) - Source: https://appshunter.io/ios/app/sight-calc/id497809138 (this page in markdown: same URL + `.md`) - Developer: [NUVOCOM INCORPORATED](https://appshunter.io/developer/497809141) - Category: Navigation, Education - Price: $1.99 - Rating: 5.00/5 from 7 App Store ratings · 17 written reviews indexed - Age rating: 4+ - Requires: iOS 16.0 · 1 MB - Languages: American English - Released: 2012-01-31 - Data updated: 2026-06-05 - Monetization: paid - User reviews in markdown: https://appshunter.io/ios/app/sight-calc/id497809138/reviews.md ## What is Sight Calc? 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 www.usps.org. In particular, this calculator is useful in conjunction with Form SR96a, www.usps.org/eddept/n/files/sr96a.pdf 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: sightcalc@nuvocom.com ## Key features - Law of Cosines sight reduction - Manual LHA, declination, and latitude input - Input as degrees/minutes or decimal degrees - Continuous computation of Hc, Z, and Zn - Supports North/South latitude and declination conventions - Clear and clear entry functions - Convert minutes to decimal degrees ## Recent user reviews (10 of 17) All indexed reviews: https://appshunter.io/ios/app/sight-calc/id497809138/reviews.md ### 5/5 — Fabulous App- Ver 2 is a much needed upgrade *2024-10-01* Wow! What a wonderful app! If you use the US Power Squadron SR96a sight reduction form this makes the math so easy. Great job on the version 2 upgrade. So much easier to use and the results are perfect. Works perfectly. Thank you. Keep up the good work. ### 5/5 — Quick Basic Sight Reduction *2018-10-18* 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! ### 5/5 — Celestial Nav Students *2017-06-17* This app is a "must" for quick and accurate solutions to the "law of cosines" ANEO ### 5/5 — Sight Calc-Don't Take JN Without It !! *2017-06-16* Slide rules and scientific calculators are not my thing. Many thanks to sight Calc for getting me through the USPS JN course! ### 5/5 — Good for USPS Navigation and Jr Navigation Courses. *2017-05-25* 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. ### 5/5 — 1.2 Works with new iOS 10 *2017-03-30* Started using this apt last year when taking USPS "JN" to check my Law of Cosigns calculator method with the old ISO and it worked with some bugs. Upgraded to the new IOS 10 and had to workaround to get the answer. New Sight Calc 1.2 update takes care of that workaround using the new IOS 10. Stilling using it in my new class USPS "N" to recheck my LOC calculations... ### 1/5 — iOS 10 issue *2017-02-12* App fails at entry of minutes in Dec line when running iOS 10. Hope they will fix! ### 2/5 — iOS 10 *2017-01-05* This is a great App for doing sight reductions using the law of cosines. I would give it a five star rating except it has compatibility issues with iOS 10. ### 2/5 — Sweet App ... But the Azimuth Can Be Wrong *2016-09-19* 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! ### 5/5 — works well *2014-12-29* 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. ## Frequently asked questions about Sight Calc ### What is Sight Calc used for? Sight Calc is a specialized calculator for performing sight reductions using the Law of Cosines method. It is particularly useful for students learning celestial navigation. ### Does Sight Calc use Nautical Almanac data? No, Sight Calc does not use Nautical Almanac data. Users must first compute the Local Hour Angle (LHA) and declination, and determine their approximate latitude before inputting these values. ### How can I input values into Sight Calc? You can input values as degrees and minutes (e.g., 44 degrees, 48 minutes) or as decimal degrees (e.g., 44.48833). The app prompts for LHA, Latitude, and Declination in sequence. ### How does Sight Calc handle North and South hemispheres? For Latitude, enter North as a positive number and South as a NEGATIVE number. Similarly, enter Declination as positive for North and negative for South. This is crucial for accurate azimuth (Zn) calculation. ### What are the key outputs of Sight Calc? Sight Calc continuously computes and displays Hc (altitude computed), Z (azimuth), and Zn (true bearing) as you enter your input values. ### Is Sight Calc available on multiple devices? Yes, Sight Calc is supported on both iPhone and iPad devices, making it accessible for users on Apple's mobile platforms. ### How often is Sight Calc updated? The latest version of Sight Calc is 2.0, which was last updated on January 31, 2024. This indicates a recent update, suggesting ongoing support and potential improvements. ### Does Sight Calc have ads? No, Sight Calc is ad-free. As a paid application, it does not contain advertisements, allowing for an uninterrupted user experience. ## Version history (last 5 releases) ### 2.0 — 2024-01-31 • 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 ### 1.5 — 2018-03-23 This app has been updated by Apple to display the Apple Watch app icon. Adjusted flipside command bar for iPhone X. ### 1.4 — 2018-03-22 Fixes rounding of Zn when Z = nnn.5 ### 1.3 — 2017-05-24 Fixes an error in the calculation of azimuth (Zn). Southern latitude must now be entered as a negative number. ### 1.2 — 2017-03-07 Now works on iOS10; calculates azimuth (Zn) as well as azimuth angle (Z). Added CE (Clear Entry) key. ## More apps by NUVOCOM INCORPORATED - [Lambi Learns](https://appshunter.io/ios/app/lambi-learns/id6496972357) All apps by NUVOCOM INCORPORATED: https://appshunter.io/developer/497809141 --- *Data collected daily from the US App Store and indexed by [AppsHunter](https://appshunter.io/). User reviews are verbatim App Store reviews. Ratings, prices and chart positions refresh continuously; this snapshot is from 2026-06-05.*