Jelajah Angka: Math Fluency
Mental math practice for children aged 7 and up through adults that measures fluency, not just correct answers — fully offline, no ads, no account.
Free · No account · No ads · Fully offline
Problem
A child who answers 7 × 8 correctly in six seconds has not memorised it; they are still counting. Until the basic facts are automatic, the fractions, percentages and algebra built on top of them stay heavy — yet school reports and most apps only see right or wrong. Parents rarely know which facts exactly are missing, and the practice apps that exist tend to demand an account, ads, or a connection from a seven-year-old.
Solution
Built a practice app that records every arithmetic fact together with its answer time, so that "memorised" means both correct and fast. A five-minute Warm-up Voyage sets the starting point with no red scores; a map of 31 islands runs from numbers to 100 up to percentages, algebra and everyday finance; facts that start to fade come back as the Fog of Forgetting; word problems are split into three stages in Detective Village; and the Report is written so a child can read it. One constraint shaped the rest: the app requests no internet permission at all, so nothing can leave the device.
The voyage, screen by screen
From the home island with its two-minute mission to a report written for the child to read.
Swipe to see more screens →
What gets trained is fluency
Each mechanic below exists for one purpose: basic facts becoming automatic, not merely answered.
A small mission daily
A two-minute Mini Mission with a clear target, streaks in the logbook, and an anchor that holds the streak through one missed day.
A map of 31 islands
Seven regions from numbers to 100 up to percentages, algebra and finance; the Warm-up Voyage sets the starting point with no red scores.
Every fact remembered
Memorised, getting fluent, or often wrong, per fact; those that start to fade return as the Fog of Forgetting.
Manipulatives first
Learn levels use place-value blocks, number lines, bar models and fraction pieces before any timed practice.
Word problems in three stages
Detective Village: mark the numbers that matter, pick the method, then calculate — and the report records the kind of mistake.
A report for the child
A mastery map, speed versus accuracy, and one suggestion; the parent section and settings sit behind an optional PIN.
The numbers behind the app
Curriculum coverage and the quality guards, counted from the code.
Levels
372across 31 islands
Seven regions, from the starter archipelago for seven-year-olds to the adult city and the champions' arena.
Trick cards
15shortcuts
Pairs of 10, double-double, ×5 via 10 and more — unlocked as they are learned in a level.
Internet permission
0not requested
The manifest declares no INTERNET permission, so Android refuses every connection from this app.
JVM tests
98tests
Question generator, mastery model, placement, and the habit engine are tested without an emulator.
What leaves the device, and what doesn't
Nothing — and the permission list proves it.
- No account, no sign-in. Profiles are created on the device; several players can share one phone.
- No internet permission. The app cannot open a connection at all, so no data can be sent anywhere.
- No ads, no analytics, no crash reporter. There is no third-party SDK in the release build.
- One permission: notifications. For the Sailing Hour reminder scheduled on the device, and it can be declined.
- Backups stay in your hands, and can be locked. All profiles go into one file through the share sheet; optionally AES-256-GCM encrypted under your passphrase.
- The parent PIN is stored as a salted hash. Only Settings is locked; the Report stays readable for the child.
Before you look for it on the Play Store
This app is not on Google Play yet. The listing, screenshots and release bundle are ready, but the release has not been submitted — which is why this page has no download button.
The "memorised" threshold in seconds is still an initial guess to be tuned after two weeks of real data, so a status shown in the Report may shift in the first version.
Jelajah Angka (“Number Voyage”) started from one observation at home: a child who answers a multiplication correctly but slowly is treated the same as one who has memorised it, when the first is still counting. So the mastery model records answer time per fact, and the Warm-up Voyage measures the same thing without ever showing a red score.
The coverage is deliberately wide — seven regions from age seven to adulthood — but the mechanics are one. An adult profile only swaps the skin for Focus Mode: five-minute sessions, no story, with daily quick-math, household finance, estimation and a numerical-test arena on top of the same engine.
The decision that shaped it most was not requesting the internet permission. Player-versus-player duels use a six-digit code sent through whatever messaging app the players already use, backups go through the share sheet, and the background music is a single CC0 file bundled with the app — so the “collects no data” line in the Play Console can be proven rather than promised. The interface is in Indonesian.
The app’s privacy policy lives on its own page.