Calculations Explained

Every number SwimLab shows you is derived directly from your marker timestamps. Here’s exactly how each metric is calculated.

Timestamps

Every marker stores a timestamp — the time of that frame in the video, measured from frame 0 in seconds to three decimal places (milliseconds).

All split calculations are simply differences between timestamps:

Split = Marker B timestamp − Marker A timestamp

There is no AI inference or estimation involved — the numbers come entirely from where you placed your markers.

Lap Splits

A lap is defined as the time between a Start and the first Turn, or between any two consecutive Turn markers, or from the last Turn to the Finish.

Lap 1 = Turn 1 timestamp − Start timestamp
Lap 2 = Turn 2 timestamp − Turn 1 timestamp
...
Final lap = Finish timestamp − Last Turn timestamp

For a 50m race there are no turns, so the only split is:

Total = Finish timestamp − Start timestamp

Total Time

Total time = Finish timestamp − Start timestamp

This is always the sum of all lap splits. If your splits don’t add up to your total time, a marker is in the wrong place.

Reaction Time

Reaction time is only shown when a Reaction marker is present.

Reaction time = Start timestamp − Reaction timestamp

Turn Cycle Time

Turn cycle is shown when a Turn marker is followed by a Breakout marker.

Turn cycle = Breakout timestamp − Turn timestamp

This measures the total time from wall touch to first stroke — encompassing the push-off, glide, underwater dolphin kicks, and breakout stroke.

Underwater Time

Underwater time is shown when a 15m marker is present after a Start or Turn.

Underwater time = 15m timestamp − (Start or Turn) timestamp

A shorter underwater time at a given 15m mark means a faster underwater phase.

Underwater Distance

SwimLab does not calculate a variable underwater distance — the 15m marker is always placed at the 15m position by the coach. The 15m marker always represents 15 metres.

What varies is the Underwater time — how fast the swimmer covered that 15m. A coach placing the 15m marker at 12m by mistake will produce incorrect metrics.

Stroke Rate (from Custom markers)

SwimLab does not auto-detect strokes. If you place Custom markers on each stroke cycle, the splits table shows the time between each pair. To calculate stroke rate from this:

Stroke rate (cycles/min) = 60 ÷ (time between two consecutive stroke markers)

Frame Precision

Timestamps are stored at the frame level — each marker is snapped to the nearest video frame. Precision depends on frame rate:

For competitive analysis, 60fps footage is strongly recommended.

Why My Splits Don’t Match the Scoreboard

SwimLab measures from your video — it is not connected to the official timing system. Differences arise from:

• Camera latency — the camera’s internal timing vs. the official touch-pad clock
• Angle — if the camera isn’t perpendicular to the pool, the touch moment may be harder to identify precisely
• Frame rate — at 30fps, a ±33ms error is possible per marker; across multiple markers this compounds

SwimLab times are analysis times for coaching purposes, not official competition times.