Sight Folder: Pub 229 Workbook — Help and questions

Sight Folder is a workbook for people who work a celestial sight by hand in NGA Pub 229. It lays out every line of the Pub 229 work form and lets you check each one. Its aim is to help you find the line you got wrong before the examiner does.

This page covers what the app does, what it cannot do, what is free and what Sight Folder Pro adds, and how to keep your saved sights safe.

What it does

Work a Sight

The screen the app opens on. You enter the entering arguments: assumed latitude with an N/S control, LHA, and declination with an N/S control. The app shows whether latitude and declination are same name or contrary name. It then works every line of the reduction in the order Pub 229 uses:

Tab Hc
d, with its sign
the d-correction, tens and units, from the Interpolation Table
the DSD correction, where the table calls for one
Hc
Z and Zn, with the rule used to turn Z into Zn written beneath them
if you enter Ho, the intercept, stated TOWARD or AWAY

Hemispheres are N and S buttons (read aloud as North and South), and the form names same or contrary name for you, so you never need the keyboard's minus key.

Your sight is saved as you type. Leaving the screen, rotating the phone or closing the app does not lose it.

If you are new to the form, the empty screen offers one of the NGA's own worked examples from the Pub 229 introductions, filled in with one tap.

Line Explainer

Tap any line of the form to see:

what that line is
where it comes from in Pub 229
the arithmetic, using your sight's own numbers
the common mistake on that line
whether the value matches a printed page we checked, or was regenerated by formula and not individually checked against print

Sight Folder

Sights you save from Work a Sight are kept here, newest first. Sights worked together are grouped into a round. Each row shows the entering arguments, the intercept, Zn and when you filed it. Tapping a row reopens the full form. It never shows an answer on its own.

Rename or delete: use the labelled ⋯ control on each row. Delete is never swipe-only.
Undo: a deleted sight leaves an Undo in its place. The Undo stays, even across a reload, until you tap it or dismiss it.
Share a round: in a web browser, sends the round as plain text through the share sheet where the browser offers one, or saves it as a text file. The app from Google Play or the App Store does not have Share yet; an update will add it.

Table Opening

The Pub 229 page opening for a latitude and LHA, laid out the way the printed table reads. It shows declination rows with Hc, d and Z, the same-name and contrary-name halves, and the C-S line. The cell your sight uses is highlighted. The page also says where that cell's value comes from: a value checked against a printed page, or one regenerated by formula.

Exam Drill

The 18 worked examples printed in the Pub 229 introductions are free to drill. Practice sights after them, Check my own sight and the drill's record ("What your drills show") are part of Sight Folder Pro; on Google Play you can try it free for a week first, with no card, and on iPhone and iPad through Apple's free trial of the yearly plan (see "Free, paid, and what stays free", below). Without Pro, each of those says so where it would be.

You type each line yourself. The table's value stays hidden until you have typed yours or chosen to show it.

Set me a sight: start with the NGA's own worked examples from the Pub 229 introductions, then practise with sights the app sets from the Pub 229 formula. Practice sights can be drawn from Vol. 2 (15°–30°), the volume named in published copies of the USCG exam-room reference list.
Check my own sight: type the entering arguments from your own homework or noon sight, plus Ho if you have one, then your own lines. They are checked the same way.

A sight you set aside waits on the drill's front page. Clear removes it.

How the checking works:

A line that disagrees with the table is flagged as soon as you enter it, on that line.
Only the first line that departs from the table is flagged as wrong. A later line that follows correctly from your own earlier numbers reads, for example, "Follows from your d-corr units." It is not blamed.
Where a table value sits right on a rounding boundary, either neighbouring tenth is accepted.
The flag tells a lookup error (the wrong row, column or section) apart from a value that is off by 0.1′.
The correct value is one tap away, with a link to that line's explainer.
The drill ends with a list of the lines that differed. There is no score, no grade and no streak.

The drill keeps a plain record by line type, for example "d-corr units: 2 of your last 5 differed". It counts line types, not you. Every finished drill is recorded on your phone; reading the record is part of Pro, and once you have had Pro it stays readable after Pro ends.

About the Tables

Found through Settings. It explains:

what Pub 229 is
where the values in the app come from
how many printed values the app has been checked against
Pub 229's own error budget

It also has a button that runs those checks again on your own phone and tells you the result.

Settings

Theme: follow the phone, light, or dark.
New sights start in: North or South latitude.
Show Ho and the intercept: on, or off to stop the form at Hc and Zn.
Your folder: add sights from a file, or clear it (with a confirmation and an undo). In a web browser you can also save it as a file; the app from Google Play or the App Store cannot yet.
Sight Folder Pro: one row under About shows what you have (the free week and when it ends, your plan, or that it has ended) and opens the Pro screen, where Restore purchases and, with a plan, Manage or cancel are.

The app's text follows your phone's text-size setting.

Where the numbers come from

The app works out Pub 229's table values from the published formula. It does not store scans of the pages. We checked those values against 154 values transcribed from the printed NGA volumes: 96 main-table cells, 40 Interpolation Table entries and 18 complete worked sights from the volume introductions. They cover Vols 1, 2, 3, 4 and 6. All 154 matched when that check was last run in the app's own test suite.

What that does and does not mean:

Vol. 5 (60°–75°) has not been transcribed yet. The app works sights at those latitudes, but no Vol. 5 value has been checked against a printed page.
Most cells in the table were regenerated by formula and not individually compared with print. The app says so on each one.
The app shows every line of the form to 0.1′ and 0.1°, as Pub 229 prints them. Only the Line Explainer's arithmetic carries more places, to show how a printed value was rounded. By Pub 229's own account, a tabulated value can be off by up to ±0.05′, and an interpolated Hc with the DSD correction by up to ±0.31′.

Pub 229 (Sight Reduction Tables for Marine Navigation) is published by the National Geospatial-Intelligence Agency. It is a U.S. Government work and not subject to U.S. copyright. Sight Folder is not affiliated with or endorsed by NGA.

What it does not do, on purpose

It does not compute GHA or declination. You bring LHA and declination from your own Nautical Almanac, as you would in the exam room.
It has no time-of-sight field or chronometer. The inputs are LHA and declination.
It does not give a position fix, a plotting sheet or a "you are here". It is a workbook for checking and drilling. It is not a navigation system, and it is not a substitute for your own working or for proper navigation equipment at sea.
It does not reproduce Nautical Almanac pages.
It uses one method only: Pub 229. There is no Pub 249, no NP 401 and no method selector.
It does not correct your sextant altitude. The form takes Ho as you type it. Index correction, dip and the main correction are yours to apply first.

What the platform cannot do

Sight Folder is built as a web app and packaged for Android, and for iPhone and iPad. A few things are simply not possible for it, and we would rather tell you than have you look for them:

No home-screen or lock-screen widget. The app is built on the web platform, which has no widget API, and it has no native widget code.
No watch app, and no Android Auto or CarPlay.
No reminders or notifications. The app does not send any, and it never asks for notification permission.

Saving, moving and deleting your data

Where your data lives

Everything stays on your phone, inside the app's own storage:

the sight in progress
your Sight Folder
your drill record
your settings

There is no account and no sign-in, and the app never sends your sights, your drill record or your settings to us or to anyone else.

That also means we cannot recover your sights for you. If you uninstall the app (on iPhone and iPad, delete it) or, on Android, clear its storage in your phone's settings, your folder goes with it. The only copies are on the phone and, if you have Android's own device backup turned on, possibly in that backup; on an iPhone or iPad, possibly in iCloud Backup (in your iCloud account, under Apple's terms) or in a backup to a computer. We have not tested whether restoring any of these backups brings the folder back, so do not rely on it. The app from Google Play or the App Store cannot save the folder as a file yet; an update will add it.

Saving your folder as a file (export)

Not in the Android, iPhone or iPad app yet. The packaged app cannot hand a file to your phone, so this version does not offer it there; an update will add saving and sharing.

In a web browser: Settings → Your folder → Save the folder as a file. The same button is also on the Sight Folder screen. It makes a plain JSON file named like sight-folder-2026-09-28.json, dated by your device's calendar. Keep it somewhere you back up.

Adding sights from a file (import)

Settings → Your folder → Add sights from a file, or the same button in the Sight Folder. Choose a file you saved earlier. Adding from a file never removes a sight you already have, and a sight that is already in your folder is not added twice. An Undo appears straight after.

Deleting your data

One sight: its ⋯ control in the Sight Folder → delete.
The whole folder: Settings → Your folder → Clear the folder. You confirm first, and an undo is offered straight after.
Everything the app keeps, including the drill record and settings: uninstall the app (on iPhone and iPad, delete it), or on Android clear its storage in your phone's app settings.

Free, paid, and what stays free

What does Sight Folder cost? The download is free, and so is everything listed under "What is free" below. Sight Folder Pro, sold through Google Play, and on iPhone and iPad through the App Store, costs $19.99 a year or $2.99 a month (US prices; the store shows yours before you confirm). On Google Play you can try it free for a week first, with no card. On iPhone and iPad, the free week is Apple's free trial of the yearly plan, for new subscribers: it is charged to your Apple Account when the week ends unless you cancel at least 24 hours before it ends. There are no ads.

What does Pro add? More of Exam Drill: practice sights after the 18 worked examples, aimed at the kind of line you missed most recently; Check my own sight, which checks a sight from your own homework or practice sheet line by line; and the record of what your drills show. Pro also gets new Exam Drill sets about every quarter, in app updates. See "Exam Drill" above.

What is free?

Work a Sight: every Pub 229 line shown, offline.
The Line Explainer, Table Opening and About the Tables.
Your Sight Folder: every sight you save, kept on your phone.
Exam Drill on the 18 worked examples printed in Pub 229.

How do the plans work?

The free week, on Android, opens Pro for 7 days with one tap, with no card and no purchase. Sight Folder offers it on the finished sheet of a drill (one of the 18 worked examples counts), from your first one until you start it or tap Not now, and the yearly plan on the Sight Folder Pro screen starts it too. Nothing is charged and nothing renews when it ends: Pro locks again, and every sight you saved still opens. From day 5, a line under the work form says when the week ends.
Yearly: Google Play charges $19.99 when you confirm, and every year after, until you cancel.
Monthly: Google Play charges $2.99 when you confirm, and every month after, until you cancel.
On iPhone and iPad, the free week is Apple's 1-week free trial of the yearly plan, for new subscribers. It starts from the yearly plan on the Sight Folder Pro screen, and $19.99 (US price) is charged to your Apple Account when the week ends, unless you cancel at least 24 hours before it ends. Otherwise the yearly or monthly price is charged to your Apple Account when you confirm. Both plans renew automatically unless cancelled at least 24 hours before the end of the current period. The free-week card on a finished drill sheet, and the day-5 line, are Android only.
There is no lifetime purchase and no weekly plan.

If I subscribe and then stop, what happens to my sights? Every sight you saved still opens on Work a Sight, the worked examples still drill, and Exam Drill's page still shows what your drills recorded. Only practice sights after the worked examples and Check my own sight ask for Pro again; a practice or own sight you left half typed is kept and listed, and waits for you.

Does it work on iPhone? Yes, on iPhone and iPad, from the App Store; see Common questions. There, purchases are Apple's, and the answers below say where to cancel, restore and ask for a refund.

Cancelling, refunds and restoring

To cancel, in two taps: open Settings and tap your plan's row, "Yearly plan" or "Monthly plan" (1), then tap "Manage or cancel in Google Play settings" (2). That opens Google Play's own subscription page, where you cancel. There is no screen of ours in between, no offer to talk you out of it, and nothing to fill in. You can also cancel any time from the Google Play app: tap your profile picture, then Payments & subscriptions > Subscriptions. You keep Pro until the end of the period you paid for.

On iPhone and iPad: in Sight Folder's Settings, tap your subscription's row (during Apple's free trial it reads "Free trial"), then "Manage or cancel in Settings", which opens Apple's own subscription page. You can also manage or cancel any time in the Settings app on your iPhone or iPad: tap the name at the top, then Subscriptions. Cancel at least 24 hours before the end of the current period to stop the next charge.

Refunds are handled by Google Play, not by us, because Google Play takes the payment. Ask through its refund page, https://support.google.com/googleplay/answer/2479637 . On iPhone and iPad, Apple takes the payment, and refunds are requested from Apple at https://reportaproblem.apple.com . Because there is no account, a subscription bought in one store does not carry over to the other.

Restore purchases is on the Sight Folder Pro screen, for a new phone or a reinstall, signed in to the same Google account, or on iPhone and iPad to the App Store with the same Apple Account.

A charge you do not recognise. On Android the free week never charges anything. On iPhone and iPad the free week is Apple's trial, and the yearly price is charged when it ends unless you cancelled at least 24 hours before. If you see a charge for Sight Folder you did not expect, check Google Play > Payments & subscriptions, or on iPhone and iPad Settings > the name at the top > Subscriptions, for a yearly or monthly plan, and tell us too.

Privacy, in short

No account, no login, no email address.
No ads and no usage tracking.
No runtime permissions. The app never asks for your camera, location, contacts, files or notifications.
Your sights stay on your phone. The app's pages can load only the app's own files, so what you type cannot be sent anywhere. Your phone's own backup (Android's, or iCloud Backup on iPhone and iPad) may include them.
If you buy Sight Folder Pro, Google Play (on iPhone and iPad, Apple) takes the payment and RevenueCat, the app's billing service, keeps the purchase record so the app knows what you own. To know that, the app asks RevenueCat soon after it starts, with a random app user ID (on iPhone and iPad, also Apple's identifier for vendor), whether or not you buy. They see the purchase, never your sights.

The full privacy policy is linked from the store listing.

Common questions

Why does my Hc differ from my calculator's or another app's? The app gives the Pub 229 hand result, the value you get by working the tables and the Interpolation Table as the book directs. A direct formula or a calculator gives the exact altitude, which can differ by a few tenths of a minute. That difference is within Pub 229's own stated error budget (up to ±0.31′ with the DSD correction). When you are checking exam work, it is the Pub 229 value you want.

The drill flagged a line I'm sure is right. Tap the line's explainer. It shows the row, column and arithmetic the app used, and whether that value was checked against print. If a table value sits on a rounding boundary, either neighbouring tenth is already accepted. If you still think the app is wrong, please tell us which volume, page and value your printed book shows. That is exactly the kind of report we want.

Can I use it at sea with no signal? Yes. The app needs no connection to work a sight, open a table page or run a drill. Buying Sight Folder Pro, restoring it, or starting the free week needs a connection once, so the app can reach the store (Google Play, or the App Store on iPhone and iPad); after that, Pro works offline, and the app checks with the store again when it next has a signal.

Does it work on iPhone? Yes. Sight Folder is on the App Store for iPhone and iPad, the same app through the same packaging, with the same free parts and the same Sight Folder Pro. One difference: on iPhone and iPad the free week is Apple's trial of the yearly plan (see the plans, above). As on Android, saving the folder as a file and Share are not in the app yet.

Do I need to update it every year, like an almanac? No. The Pub 229 values do not change from year to year, so there is no annual data to buy or download.

Getting in touch

Please write to support@chibuapps.com, the developer contact email shown on the Google Play listing; it is the same address for the iPhone and iPad app. It helps to include:

your phone or iPad model, and its Android or iOS version
which screen you were on
for a number you think is wrong: the entering arguments, the line, and the value your printed Pub 229 shows, with volume and page

A report of a number that disagrees with the printed book is the most useful thing you can send us.

Who makes this

Sight Folder is published under the developer account named on its Google Play and App Store listings. It carries no advertising. Its one service provider is RevenueCat, which keeps purchase records for the app (see the privacy policy). The app was built with the help of AI coding tools. Its numbers are held to account by the printed tables, through the 154-value check described above, rather than by anyone's say-so.