Summa

A notepad calculator for Googlebooks and Android.
Type maths the way you'd say it: Hotel: 3 nights × $142 in EUR. Answers line up on the right as you type.

⬇ Download Summa.apk  ·  Install  ·  What you can type  ·  Privacy  ·  What's new

_{A personal hobby project by Fika Labs, proudly developed on a Googlebook. Not affiliated with or endorsed by any employer (more). Inspired by Soulver and Numi.}

What it does

Summa is a sheet of paper that does the maths. Write a line in plain words and the answer appears next to it, on the right. Change a number and everything that depends on it updates. Nothing else gets in the way: no toolbars, no pop-ups, just the sheet.

• Words around numbers are fine. Lunch: $12 + 15% tip, Flights: 2 × €189. Summa skips the words it doesn't know and works out the rest. A line that isn't maths simply has no answer.
• Units and money. 5 km in miles, 72 °F in °C, €49 in USD, 6.4 L/100 km in mpg, $25/hour × 14 hours, 1 cm in px at 326 ppi.
• Percentages, every way. 20% of $10, 5% on $30, 6% off 40 EUR, $50 as a % of $100, 20 is 10% of what, 50 to 75 is what %.
• Dates and time zones. days until Christmas, next friday + 2 weeks, 8:30 am + 3 h 20 min, 3 pm Munich in Tokyo, time in Japan. Over 6,000 cities, every country and the usual abbreviations (PST, CET, IST…), all offline.
• Live exchange rates for 166 currencies and metals, refreshed twice a day, with rates built in for offline use. Crypto if you want it.
• Money over time. $10,000 at 5% for 10 years compounded monthly, interest on €60k at 2.5% for 3 years, loan of $300k at 6% for 30 years (→ $1,798.65/month), and tax both ways: €1,350 incl 19% VAT, €120 without 20% VAT.
• Workdays and public holidays. workdays until Dec 18, 5 workdays after Dec 22, workdays between Oct 1 and Oct 31, next holiday. Summa knows the nationwide holidays of 22 countries and skips your region's (Settings › Public holidays).
• Your own names. rate = $85/hour, then rate × 6.5 hours. Refer to a line with line6, the line above with prev, and add up a block with sum.
• Your own units and functions. 1 tin = 2.5 L, then 7.2 L in tins; 1 coffee = $4.50, then $20 in coffees; tip(bill) = bill × 18%, then tip($86). Put them on the Definitions sheet (Settings › Definitions) and they work in every sheet.
• Formats. 255 in hex, 0.2 as fraction, 1/3 to 2 dp, $490 rounded to nearest hundred.

_{Mortgage, VAT, savings, workdays and a home-made unit, in dark mode.}

Click an answer to copy it; right-click it to copy the line or convert it to another unit or currency. As you type, a suggestion for the word appears in grey after the cursor: Tab takes it. In a desktop window your sheets are listed on the left, newest first (Ctrl+B hides the list). The Share button copies the sheet with its answers, shares it as text or PDF, exports it (PDF, web page, CSV, Markdown or text) or prints it. Five colour themes (Tangerine, your wallpaper, Cobalt, Lime and Berry), light and dark.

Made for the Googlebook

  
_{The mini calculator, pinned on top of your other windows, and Calculate on a selection in any app.}

• One calm bar on top. The window's own title bar (app handle, window buttons) is painted to match Summa's header just below it, with the sheet title, the mini calculator, Share and ⋮.
• A mini calculator that stays on top. Open it from the header or Ctrl+Shift+M and the sheet you're on moves into a small window while the big one makes way; its ⤢ button (or Ctrl+Shift+M again) brings the big window back, on the same sheet. The Quick Settings tile and the launcher open it too, on the sheet you had open last. On Android 17 desktops it stays above your other windows (its pin, or Settings).
• "Calculate" in every app. Select €49 in USD in Chrome or any app, right-click › Calculate, and a small card shows the answer with Copy, Insert answer and Open in Summa.
• A window per sheet. Right-click a sheet › Open in new window, or use the taskbar's New window.
• Drag answers into Docs, Gmail or another sheet. Share text to Summa to start a sheet.
• Keyboard first, with every shortcut listed in the system's shortcut helper (Search+/).
• Handoff: start a sheet on your phone and carry on at the Googlebook (Android 17).
• Phones too: the same quiet sheet with the system keyboard, and your sheets one tap away.

What you can type

You type	Summa answers
Hotel: 3 nights × $142 in EUR	€375.17
$10 for lunch + 15% tip	$11.50
20% discount off $500	$400.00
5 feet 11 inches in cm	180.34 cm
313 km × 6.4 L/100 km	20.03 L
€30/day in €/month	€913.11/month
days until Dec 25	86 days
2:30 pm HKT in Berlin	8:30 am
0x9F31 to decimal	40,753
average of 36, 42, 19 and 81	44.5
loan of $300k at 6% for 30 years	$1,798.65/month
€120 without 20% VAT	€100.00
1 watermelon = 20 lb, then 100 kg in watermelons	11.02 watermelons

Over 370 more examples, taken from the Soulver and Numi documentation, run as tests on every build (engine/src/test/resources/corpus.tsv).

Install

Summa is made for Googlebooks (Googlebook OS, Android 17) and also runs on Android 12 or newer phones and tablets.

1. On your Googlebook or phone, download Summa.apk from the latest release.
2. Open it from Chrome's downloads or the Files app. If Android asks, allow Chrome (or Files) to install apps, then tap Install.
3. Open Summa. It starts with a short welcome sheet and an example trip budget.

To update, install a newer Summa.apk over the old one. Your sheets stay.

Keyboard

Keys	Does
Search+/	See every shortcut (the system's shortcut helper)
Ctrl+N	New sheet
Ctrl+Shift+N	New window
Ctrl+Shift+M	Swap to the mini calculator, and back
Ctrl+K	Search sheets
Ctrl+Shift+C	Copy the current line's answer
Ctrl+/	Turn lines into notes (and back)
Ctrl+D	Duplicate the line
Alt+↑ / Alt+↓	Move the line up or down
Ctrl+\	Insert prev (the answer above)
Ctrl+B	Show or hide the sheet list
Ctrl+,	Settings
Ctrl+P	Print, or save as PDF
Esc	Clear the search, then back to the sheet; leave Settings
Tab or → / Esc	Take or hide the grey suggestion after the cursor

Privacy

Summa keeps your sheets on your device, in the app's own storage, and Android's backup copies them to your Google account if you have backup turned on. There are no accounts, ads or analytics.

Summa's only use of the internet is downloading exchange-rate tables, at most twice a day and only while Settings › Money › Live exchange rates is on:

• fiat rates from Frankfurter (central-bank rates, open source), with the European Central Bank's daily rates as a fallback;
• crypto prices from CoinGecko only if you turn on Crypto prices.

Nothing is ever uploaded: the requests carry no sheet content, account or device ID. The full privacy policy says the same in more words. With the switch off, Summa uses the rates bundled in the app (and whatever it downloaded last), and works fully offline. City and time-zone lookups are offline too.

Developed on a Googlebook

Summa is developed on a Googlebook, in its built-in Linux Terminal:

• The calculation engine is plain Kotlin, tested with JUnit in the Terminal in a few seconds. A 2,000-line sheet re-evaluates in about 50 ms on the Googlebook.
• Public holidays are computed from rules (Easter, "last Monday in May", substitute days), so there's no holiday data to download.
• The app is Kotlin and Jetpack Compose with Material 3 Expressive, built with Gradle in the same Terminal and installed on the Googlebook's own Android over adb.
• Screenshots in this README are the app's own window, captured on the device.

_{With a little help from Claude.}

Build

Needs JDK 21 and the Android SDK (platform 37).

./gradlew :engine:test            # the calculation engine and its 386 examples, no device needed
./gradlew :app:assembleDebug      # app/build/outputs/apk/debug/app-debug.apk
./gradlew :app:assembleRelease    # signed if ~/.config/summa/keystore.jks and keystore.pass exist

Builds you make yourself are signed with your own key, so install them in place of a release (uninstall first) rather than over it. ./summa is the development helper (build, install, test hooks, window captures) for a Googlebook connected over Wireless debugging. CLAUDE.md explains how the code is organised, and docs/RELEASING.md how releases are made.

About this project

Summa is my personal hobby project, published as Fika Labs. It has no affiliation with my employer: my employer didn't make, sponsor, review or endorse it, and Summa doesn't endorse my employer or its products either. The views, choices and any mistakes here are mine alone.

Summa is inspired by Soulver and Numi, two lovely Mac apps that showed how good a notepad calculator can be. It's an independent project and isn't made by or affiliated with Acqualia (Soulver) or Numi's maker.

— Fika Labs

License

Summa is free software under the MIT License. It includes the following, listed with their licences in THIRD_PARTY_NOTICES.md and in the app (Settings › About › Open-source licences), which also shows the full licence texts:

• Summa Sans and Summa Mono: Google Sans Flex and Google Sans Code, subset and renamed as the SIL Open Font License 1.1 allows.
• Google's Material Symbols (Apache License 2.0).
• Exchange rates from the European Central Bank (source: ECB), bundled for offline use.
• City data from GeoNames (CC BY 4.0): cities of 100,000+ people and capitals.

It uses Jetpack Compose, AndroidX, Kotlin, kotlinx.coroutines and kotlinx.serialization (Apache License 2.0, full text).

A kit for publishing on Google Play (listing text, graphics, policy answers) is in store-submission/.