Drift read

The drift read puts the start of a piece next to its end. It shows how each stroke reading moved between the first quarter and the last quarter, and nothing else.

What it comparesCopy Anchor Link

A piece is cut into quarters of its usable work strokes. The read compares the first quarter with the last. The chart says by quarter. On an interval piece it compares the first interval with the last, and the chart says by interval. Select an interval and the read covers that interval, cut into its own quarters.

Some strokes are left out first:

• Rest strokes.
• The first three strokes of each interval. The monitor under-reads them, and the flywheel is dead or still spinning up.
• Strokes whose drive time is more than 1.5 times the median drive time. The median is for what is on screen: the selected interval when you pick one.
• Strokes whose drive time is less than the median drive time divided by 1.5. When you stop in the middle of an interval, the PM5 can send short strokes with almost no drive. This rule removes them.
• Strokes with no drive time, including a logged 0. This applies when at least half the strokes carry a drive time. When fewer do, as on the BikeErg, no drive-time exclusion happens.

At least 40 usable strokes are needed. Below that, the read is not shown.

When it shows nothingCopy Anchor Link

A read is never built from part of a piece as if it were the piece. It is not shown in any of these cases:

• The capture was truncated.
• The capture covered less than 80% of the piece.
• The capture has a gap longer than a minute inside a work interval.

A workout synced from the Concept2 Logbook has strokes. It does not have the per-stroke distance and force the PM5 sends, so it has no drift read.

The readingsCopy Anchor Link

Each reading is the median over the quarter, or over the interval on an interval piece. It is not the mean.

• Work per stroke (J): average drive force times drive length. When fewer than half the strokes carry handle data, it is watts times 60 divided by rate. The BikeErg sends none. A piece uses one route, never both.
• Peak force (lbf or N): the highest force in the drive, in the unit you set.
• Peak position (% of the drive): where the peak falls, taken from the raw samples.
• Drive length (m).
• Drive / recovery: drive time divided by recovery time.
• Meters per stroke (m).
• Rate (spm, rpm on the BikeErg).
• Watts (W).

On the SkiErg the stroke is a pull, and on the BikeErg a revolution. The labels follow the machine.

The change is shown for every reading. A change is bold when it passes a fixed threshold:

• 5% for work, peak force, drive length, meters per stroke and watts.
• 5 percentage points for peak position.
• 0.10 for drive / recovery.
• 2 spm for rate (rpm on the BikeErg).

Bold means the change is large enough to read, not that it is good or bad.

Rate and work per strokeCopy Anchor Link

At fixed power, work per stroke has to fall as rate rises. It follows watts × 60 ÷ rate. If watts held, a ▼ on work per stroke beside a ▲ on rate is that arithmetic. A fall larger than watts × 60 ÷ rate predicts is the part worth reading. Rate is always in the table so you can judge.

What it cannot tell youCopy Anchor Link

• Body position or technique. A force curve can be consistent with a fault. It cannot name one.
• Whether a change is fatigue or intent. A planned rate rise and a fade can produce the same numbers.
• Anything about another athlete. Every change is against your own first quarter. There is no population norm, and no number is called good or bad.