If every clock disagrees a little, which one is right?

Picture the classic setup. A finish camera on one side of the track, a backup camera on the other, a start device up the course. To keep them honest, someone runs a dedicated timing cable from camera one, across the track, over to camera two — a physical link per pair of devices. Add a third camera and you add another run of cable. The infrastructure grows faster than the event does.

And underneath the cabling sits a subtler problem: each of those devices has its own clock. The start gun's clock. The finish camera's. The backup's. The timing box in the truck. Each is accurate on its own — and each is drifting, by microseconds, away from the others. For most of sport that gap is invisible. In a photo finish, microseconds are the whole game.

So there are really two questions hiding in one: do all my devices keep the same time — and do I have to keep pulling cable to make them?

The grandmaster is not a box you buy — it's the device that already knows the time best

There's a protocol built for exactly this: PTP, the Precision Time Protocol. Its job is to take one clock on the network and make every other device follow it — not roughly, but to a fraction of a microsecond. The clock that leads is called the grandmaster.

Here's the part people expect to be complicated and isn't: the grandmaster isn't special hardware. It's simply whichever device on the network holds the best time — and then announces it. Our camera is already disciplined by satellite: a GNSS receiver feeds it a pulse once a second, anchoring its clock to atomic time from space (that's the GPS story). A device with time that good has no business following anyone. So it leads. The camera becomes the grandmaster, and everything else on the field sets its watch by the camera.

GPS put the right time inside one device. PTP hands that time to all of them.

The consequence nobody expects: the cable length stops mattering

The obvious objection to "share time over a network" is that a network takes time to cross. A signal down a longer cable arrives later — so wouldn't a device further away end up slightly behind?

It would, if PTP just shouted the time and hoped. Instead it measures the trip. Grandmaster and follower exchange a few timestamped messages, work out exactly how long the wire delay is, and the follower subtracts it. The result: a device three metres away and a device thirty metres away end up on the same time, because each has cancelled its own path delay. You stop caring where a camera sits on the field. Add one, plug it in, and it's in sync — no calibration ritual, no re-laying anything.

One network instead of a web of cables

This is where the dedicated timing cable quietly disappears. Camera one and camera two no longer need a wire strung between them across the track — they only need to be on the same network. Camera two joins that network and becomes a follower of camera one, the grandmaster. Want a third camera, or the start device on the same clock? Plug it into the network. You grow by adding a port, not by pulling another cable end to end.

Two things have to be true for the microseconds to hold, and they're worth stating plainly. The network switch must understand PTP, so it accounts for its own tiny delay instead of smearing the timing. And each device needs a network card built for PTP — one that timestamps in hardware, at the wire, rather than letting software guess. Lion Timing's devices carry that hardware; it's what lets a camera keep time this precisely for everything downstream of it.

And then the part that makes the whole approach pay off many times over: it's the same network you already use for everything else. The cable that carries the timing sync is the cable that sends the finish time to the scoreboard and the dashboard — and the cable that streams the camera's image back to the laptop. Time, results, and picture all ride the one network. There's no parallel world of timing-only wiring to plan, lay, and protect. This is simply the modern way timing devices are linked, and it's the shape of setup that scales without turning the venue into a cable diagram.

And if you'd rather not change a thing, you don't have to: the traditional way of running a separate cable between cameras still works exactly as it always has — the network is simply the easier option when you want it, never a new system you're forced to learn.

What if the grandmaster fails?

A leader everything depends on sounds like a single point of failure. PTP's answer is an election. Every capable device advertises how good its clock is; the network continuously picks the best one as grandmaster (the "best master clock" rule). Lose the lead camera and the next-best clock steps up automatically, and the field keeps agreeing. The role is inherited, not owned.

Quick check

Next in the Academy: Multiple cameras: one race, several angles, one clock →