Comparison

Atomic Clock vs ThreeDay Calendar

Price, ratings, monetisation and update history for both apps, side by side — with what reviewers say about each.

Head to head
About

Atomic Clock

This utility provides highly accurate time synchronization using NTP, displaying precise time with millisecond detail. It allows comparison with network time, shows sync offset and latency, and offers various clock styles with customization options. It's designed for users needing a reliable, precise reference clock.

Highlights
  • NTP-based time synchronization
  • Millisecond time detail
  • Local time and UTC display
  • Device offset and network latency indicators
  • Automatic sync
  • Multiple clock styles
  • Customizable colors and night mode
Features
Read full description

Atomic Clock – Precision Time is a professional precision clock and NTP time synchronization utility for anyone who needs highly accurate time directly on their device. Use reliable network time synchronization to view precise time with millisecond-level detail. Compare your device clock with network time, check sync offset and latency, switch between local time and UTC, and keep the screen on when you need a stable reference clock. Key features: • NTP-based time synchronization • Millisecond or 1/60-second detail • Local time and UTC display • Device offset and network latency indicators • Automatic sync with configurable intervals • Six clock styles: circular dots, analog, minimalist, binary, neon glow, and flip clock • Custom accent colors and multi-color display • Night mode and keep-screen-on option • Privacy-focused: no account, no analytics, no tracking Atomic Clock – Precision Time is built for precise timing, clock drift checks, latency awareness, and a clean daily precision clock. Terms of Use https://www.apple.com/legal/internet-services/itunes/dev/stdeula/

About

ThreeDay Calendar

Features
Read full description

ThreeDay Calendar is built around the next three days: today, tomorrow, and the day after tomorrow. Instead of opening a full month grid every time, you can scan what matters now in a simple 3-day timeline. Key features - See today, tomorrow, and the day after tomorrow at a glance - Show events from calendars connected to your device, including iCloud, Google, Exchange, local, and shared calendars - Create local events or save directly to writable device calendars - Add title, start time, end time, repeat, location, reminder, and description - Search titles and notes across local and device calendar events - Hide calendars you do not need and rename calendar labels inside the app - Use event templates for repeated forms of events - Choose light, cream, or dark theme - Premium: home screen widgets for today, tomorrow, the day after tomorrow, and event cards - Premium: replace the ad area with a memo, photo frame, or D-Day display Privacy and data Your schedule data stays on your device. The app does not store your events on a separate server. Calendar access is used to show and write events through iOS device calendars when you allow it. Note Calendar sharing permissions are managed in Apple iCloud Calendar, Google Calendar, Exchange, or the calendar service you use; this app displays shared calendars that are already connected to your device. Terms of Use (EULA): https://www.apple.com/legal/internet-services/itunes/dev/stdeula/

Screenshots

Atomic Clock4 screens
ThreeDay Calendar4 screens

Verdict

The call

The clearest difference is ads: Atomic Clock at none against ThreeDay Calendar's shown. ThreeDay Calendar's advantage is update cadence (fortnightly vs every 6 weeks). On price, in-app purchases, device support and iOS requirement there is nothing between them.

Scored on Price · Rating · Positive reviews · Number of ratings · Update frequency · Ads · In-app purchases · Monetization · Best chart rank · Devices · Requires iOS

CostPrice · In-app purchases · Ads · Monetization

Both are free to download. Atomic Clock sells 2 in-app purchases, starting at $5.99 per month and ThreeDay Calendar sells 2 in-app purchases, starting at $0.99 per month. Whichever you choose, the download price is not the number that matters.

UpkeepUpdate frequency

Atomic Clock ships an update every 6 weeks, ThreeDay Calendar fortnightly. The most recent releases landed on September 18, 2026 and August 23, 2026 respectively.

Scorecard2 real differences · 8 level
Atomic Clock versus ThreeDay Calendar: the parameters behind the verdict, then further details
ParameterAtomic ClockThreeDay Calendar
PriceFreeFree
Rating4.8 (4 ratings) — better—
Positive reviews100.0% of reviews—
Number of ratings4 — better—
Update frequencyEvery 6 weeksFortnightly — better
AdsNo — betterYes
In-app purchasesYesYes
MonetizationFree with in-app purchases—
DevicesiPhoneiPhone, iPad — better
Requires iOS17.6 — better18.0
Further details — not scored
Size9 MB6 MB
Age rating4+4+
Developer家宝 戴Hoein Song

In-app purchases

2 purchases

Atomic Clock

Subscriptions2
  • AtomicClock Pro Monthly7 Days trial$5.991 Month
  • AtomicClock Pro Monthly7 Days trial$19.991 Year
2 purchases

ThreeDay Calendar

Subscriptions2
  • ThreeDay Premium Monthly$0.991 Month
  • ThreeDay Premium Yearly$9.991 Year

Questions

Is Atomic Clock free?
Atomic Clock is free to download, with in-app purchases available.
Is ThreeDay Calendar free?
ThreeDay Calendar is free to download, with in-app purchases available.
Do Atomic Clock or ThreeDay Calendar have ads?
ThreeDay Calendar shows ads; Atomic Clock does not.
Which is updated more often, Atomic Clock or ThreeDay Calendar?
Atomic Clock ships an update every 6 weeks, and ThreeDay Calendar fortnightly. Most recently, Atomic Clock was updated on September 18, 2026 and ThreeDay Calendar on August 23, 2026.

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