Swimming Pace Clock Timer

Swimming times sets on send-off intervals rather than on rest. A set written as 10 × 100 on 1:30 means a swimmer leaves every ninety seconds regardless of how fast they swim — the faster the swim, the more rest. Nobody in the pool is timing rest, and the pace clock on the wall shows only elapsed time.

The send-off is chosen so that a swimmer gets a target amount of rest at their goal pace. If your 100 takes 1:20 and you want ten seconds of rest, the send-off is 1:30. That coupling is the whole design: as you get faster, the same set automatically gets easier, so the coach tightens the send-off rather than the distance.

Reading the clock

A pace clock has a sweeping hand and a sixty-second face. Swimmers leave on the top, on the sixty, or on any marked point, and the convention is to state the departure point — 'leaving on the top' or 'on the thirty'.

The skill being learned is arithmetic under fatigue: knowing you left on the twenty, arrived on the forty-five, and therefore swam 1:25 without a stopwatch. Squad swimmers do this automatically; it takes a few weeks to become automatic.

Rest shrinks as the set goes on

A send-off set is self-regulating in an unforgiving way. As you tire, your swim slows, so your rest shrinks, so you tire faster. A set that was comfortable for the first four repeats can collapse by the eighth.

That is a feature — it is precisely how the set trains pacing discipline. The correct response is to swim the early repeats slower than you could, which is the same lesson as every other pacing page on this site.

Choosing send-offs honestly

A send-off that leaves you three seconds of rest is not a hard set, it is a failed set — the intensity drops because there is no recovery, and the training target is missed in both directions.

For aerobic work, ten to twenty seconds of rest at goal pace is a reasonable target. For sprint work, much longer rest and a much faster swim. Setting the send-off from what you can actually hold, not what you would like to hold, is the difference.

Send-offs giving roughly ten to fifteen seconds of rest for a 100 at the stated pace. Adjust upward for sprint sets and downward as you get faster.

Send-off intervals by 100m pace
100m pace	Aerobic send-off	Threshold send-off	Rest at pace
1:10	1:25	1:20	10–15 s
1:20	1:35	1:30	10–15 s
1:30	1:45	1:40	10–15 s
1:40	1:55	1:50	10–15 s
1:50	2:05	2:00	10–15 s
2:00	2:20	2:10	10–20 s

Rest shrinks as you tire, so a set that feels easy for four repeats can collapse by the eighth — swim the early ones slower than you could.
A send-off leaving three seconds of rest is a failed set, not a hard one: intensity drops and both training targets are missed.

Source: Send-off interval conventions are established swim coaching practice rather than a published standard

Sources

Send-off interval conventions are established swim coaching practice rather than a published standard , TheTimerLab — accessed 2026-07-28

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❓ Frequently Asked Questions

What does '10 × 100 on 1:30' mean?

Ten repeats of 100 metres, leaving every ninety seconds regardless of how fast you swim. The faster the swim, the more rest — swimming times sets on send-off intervals rather than on rest.

How do I read a pace clock?

It has a sweeping hand on a sixty-second face. You note where you left and where you arrived, and subtract. Knowing you left on the twenty and arrived on the forty-five means you swam 1:25 — no stopwatch involved.

Why does swimming count send-offs rather than rest?

Because it couples pace to recovery automatically. As you get faster on the same send-off you earn more rest, so the coach tightens the send-off rather than changing the distance — the set scales with your fitness.

Why does a send-off set get so much harder near the end?

Because as you tire your swim slows, so your rest shrinks, so you tire faster. It compounds. The correct response is to swim the early repeats slower than you could.

How much rest should a send-off leave?

For aerobic work, roughly ten to twenty seconds at goal pace. Sprint sets need much more. A send-off leaving three seconds is a failed set — the intensity collapses and neither target is trained.

How do I pick a send-off if I am training alone?

From what you can actually hold rather than what you would like to hold. Time a few 100s at the pace you intend to repeat, add your target rest, and round to something you can read easily on the clock.