LapLync 사용 가이드

LapLync starts stopwatches on several devices at the same moment and records laps and split times. It runs on iPhone and iPad, and people join with a six-digit room code or a QR code, with no account. It is made for people who need a shared starting instant to make times comparable: a coach measuring athletes on the sideline, or an event official logging results at several points. This guide covers the basic workflow, what happens when the connection is shaky, and how records are kept.

What problem does it solve?

Pressing several stopwatches at once is harder than it sounds. Even with a "go" call, reaction times differ, and one person cannot touch every device. When the results are compared, they are often a fraction of a second to a full second apart, which blurs comparisons between athletes.

In LapLync, when one device presses start, every device in the room shares the same start time. Each device computes elapsed time from a clock corrected against network time, so the delay in delivering the start signal does not change the reference point. The store description says this correction aims at tens of milliseconds.

Who is it for?

• Coaches and trainers who hand phones to several athletes and record laps.
• Event recorders and officials who place a device at each segment and need simultaneous timing.
• Experiments or observation exercises that record events at several places on one time base.
• Friends who want a simple record of a race from a shared start line.

Screens at a glance

The five images below are store screenshots with a promo headline on top; the screens are the iPhone app. Read them in order: create a room, start, and watch laps build up.

How to use it

1. Create a room

1. On the device that will run the session, create a room. A six-digit code and a QR code appear.
2. On the other devices, tap Join Room and enter the code or scan the QR code.
3. Check that every device appears in the participant list.

2. Start and record laps

When you press start, a 3-2-1 countdown shows on every screen and the stopwatch begins at the same moment. During the run, the lap button records a segment time, and the app arranges laps and split times automatically. No extra equipment or handwritten notes are needed.

3. Stop and review

When the measurement ends, stop it and review the results. Past sessions stay in the history screen. On the free tier the three most recent sessions are stored on the device. Pro keeps session history without a limit and lets you export it as CSV.

Staying accurate when connections are unreliable

On site, Wi-Fi is often weak and phones sometimes drop into standby. LapLync layers its connections in three steps.

• Devices in the same place use a local Bluetooth and Wi-Fi connection first.
• If devices are on different networks, it switches to an internet relay automatically.
• If every connection is lost, each device keeps measuring against its corrected time reference, and the records merge automatically when the connection returns.

So even when a reconnecting banner briefly appears, the stopwatch does not stop. No tool can promise perfection in every environment, so for an important event, run a rehearsal first.

Free versus Pro

There is a one-time Pro unlock, not a subscription. For free you can create a room of two devices and join rooms created by others without a limit on how often. Simultaneous start, lap recording, split times and all connection modes are included for free. Pro adds rooms of up to eight devices, CSV export and unlimited session history. Only the person who creates the room needs Pro, and participants never have to pay. See the store page for the current price.

A field example: one coach, four athletes

Imagine timing laps for four athletes on a 400 m track. This is an illustration of how the app features fit together and has nothing to do with the rules of any particular competition.

1. The coach creates a room on their own phone and turns on the PIN. Free allows two devices, so to connect all four, the coach who creates the room needs Pro. It is safer to unlock Pro before creating the room. Whether a purchase made mid-session immediately raises the capacity for remote connections is still listed as an open item in the development notes.
2. Three recorders scan the QR code with their phones to join. Check that all four devices appear in the participant list.
3. At the start line the coach presses start, 3-2-1 shows on every screen, and the stopwatches begin at the same moment.
4. For each lap, the assigned recorder presses the lap button. Agreeing in advance that "device 1 is lane 1" makes sorting easy.
5. When it is over, the coach stops the session and reviews laps and splits on the history screen. With Pro you can export CSV and sort by athlete in a spreadsheet.

This does not replace precise official timing. The app's clock correction reduces the gap between devices' start times, but the reaction delay of whoever presses the lap button remains. Think of it as a tool for practice, training logs and informal races.

Tips for good results

• Before starting, confirm every device is in the participant list. A device that is missing may not receive the same start signal.
• Assign each device a segment or athlete in advance so that records are easy to sort later.
• Check battery level and auto-lock. Measurement is designed to continue when the screen turns off, but a dead battery ends it.
• Exported CSV files can be shared through AirDrop, mail or other apps, so make a backup copy right after measuring.
• Devices in the same place get the fastest local link. Far-apart devices use the internet relay and may see slightly more delay.

Limits and known issues

• It is for iPhone and iPad only. It needs iOS 17 or later, and Android and Windows devices cannot join a room.
• The time correction is a target. It aims at tens of milliseconds using network time (NTP) but is not a guarantee, and it does not replace dedicated timing equipment or certified systems such as photo-finish gates.
• The human press is the largest source of error. Even if the app narrows clock drift, the reaction delay of pressing the lap button cannot be removed, so have the same person press by the same rule.
• Nearby devices use a local link, and distant ones use the internet relay. The local link supports up to eight devices, and the relay path can add a little more delay.
• Participants cannot start, stop or reset. As the on-screen note says, those three are host-only and participants can only record laps.
• Free mainly shows the three most recent sessions. Older records open without limit on Pro. Export what you need at a moment you choose.
• It is not perfect in every environment. Each device is designed to keep measuring through a disconnect and merge on return, but rehearse before an important event.

Troubleshooting

• QR scanning does not work: check that camera permission is allowed, or type the six-digit code instead.
• A third device cannot join: if the device that created the room is not on Pro, the room holds two devices.
• Times differ by seconds from another device: make sure date and time are set automatically and that the device has been online at least once.
• A record seems to be gone: the free tier keeps only the three most recent sessions. Export what you need with Pro or copy it elsewhere.

Privacy

The app has no accounts and no ads, and it does not collect location or contacts. A device identifier and device name are used to tell devices apart inside a room, kept temporarily only while the room is active and deleted when the session ends. See the privacy policy for details.

How it compares

For training and informal races LapLync is often enough, and for certified results dedicated equipment is the right tool. The background on how several devices agree on time is in our article on synchronized timers.

Sources and further reading

1. IETF RFC 5905: Network Time Protocol Version 4
2. Apple Developer: Multipeer Connectivity
3. Apple Developer: TN3179 Understanding local network privacy

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