Constantin reads the same workout data your watch already records and picks
the right movement metric for your sport: pace for road, track, and treadmill
running; NGP (grade-adjusted pace) for trail, vertical, orienteering, obstacle,
and adventure activities; speed in km/h for other recognised activities. NGP
uses the Minetti (2002) running-cost polynomial, with the ratio of vertical
to ground speed clamped to ±45%.
Every minute, Constantin saves the average pace (or speed) and heart rate of
that minute. The chart compares those minutes with right now: each point shows
whether that part of the workout was faster or slower, and whether your heart
rate was higher or lower, than it is at this moment. The numbers on the right
answer a different question: how your current value compares with your
average since the end of your warm-up.
The four points before the dot group minutes and widen towards the past:
one minute each at first, then 4-2-1-1, 8-4-2-1 and 16-8-4-2 minutes once 8, 15
and 30 minutes after your warm-up are complete (at 18, 25 and 40 minutes with the
default 10-minute warm-up). The chart reaches up to 30 minutes back, so slow
drift has time to show, while the last minutes keep their detail. The groups
follow one another without overlapping and never reach back into the warm-up;
the minute in progress is shown only by the dot.
One step up or down is always one steady range, so noise inside that range
keeps the line flat. There are four steps above and four below the centre.
Bigger differences, such as the end of the warm-up, stay on the outermost step and never
squash the rest of the line. Each line has its own steady range, so pace and
heart rate never share one numeric scale, but both end on the centreline at
the right.
For the nerds — the exact numbers:
- Evaluation: the system calls the app at about 1 Hz; full sports calculations and chart samples run every other call, at about 0.5 Hz.
- Transport: one phase calculates a complete snapshot and publishes changed movement and heart-rate values; the next phase publishes the drift packet that triggers one coordinated UI update.
- Reference averages: at first, pace is 1000 divided by the watch's average speed in m/s; speed uses that average converted to km/h, and HR uses the watch's average heart rate. NGP instead averages valid grade-adjusted speed samples collected by Constantin, then converts that average to pace. From the first valid sample after the warm-up, each reference switches to the mean of valid samples since the end of the warm-up, and the chart groups are sent again; with the warm-up set to 0 the workout averages stay. The reference drives the average shown on the Constantin screen, the delta, the status and the transport of chart points. The workout summary's AVG values stay the workout averages, while VAR averages the distance of each sample from the reference in use at that moment.
- Minute averages: one interval counts 30 calculation cycles, including cycles with missing readings, and closes when the next one starts. At the usual cadence this is about one minute of active workout time, not a wall-clock timer. Each interval stores the mean pace (s/km), speed or heart rate itself, not its drift. After the first valid reading, the last valid value also contributes during missing readings. Before that, the metric's intervals remain empty.
- Window: four historical points plus a fifth point for the current drift. Oldest to newest, the points group 1-1-1-1 completed minutes at first, then 4-2-1-1, 8-4-2-1 and 16-8-4-2 once 8, 15 and 30 minutes after the warm-up are collected. The warm-up is the first 10 completed minutes by default (setting: 0–20); a wider window is used only when it fits entirely after it, so the warm-up leaves the chart once the 1-1-1-1 window has passed it and never returns. With 0 the switches happen at 8, 15 and 30 minutes. All four groups are adjacent and end at the latest completed minute. They are drawn evenly spaced, so the left part of the chart covers more time. The unfinished minute is not included in their averages; the endpoint reflects current conditions instead. Intervals are approximate because they count calculation cycles.
- Grouping: valid minute averages in a group have equal weight. The app sends each group as its mean minus the current reference average, the same reference as the live drift, so the vertical gap between a point and the endpoint is that group's mean minus your current value. Earlier versions stored each minute's drift against the running average, which kept moving with the history and showed steady drift at about half its size. A group with no data breaks the line; the series stays hidden until its first valid value arrives.
- Collection: the app logic keeps the last 30 completed minutes of both histories for the whole active workout, whether or not the Constantin screen is visible. Pausing the workout pauses collection. The screen keeps only the five drawn points per series: the app computes the four groups itself and sends them after every completed minute and whenever the screen is shown or rebuilt, so a full chart returns within about 15 seconds. Switching between pace, NGP and speed clears only the movement history.
- Refresh: ordinary chart updates are limited to about once every four seconds, while numbers update about every two seconds and are reformatted only after a value or mode change. Screen activation, view or metric changes, a visible series gaining or losing data, and the end of each four-point history update force a chart refresh. Changes confined to the hidden series do not trigger ordinary chart updates.
- Chart limits: chart points and the endpoint are clamped to ±270 s/km (±27 km/h in speed mode) and ±90 bpm from the reference average. These are chart limits, not limits on the displayed current and average values.
- Steady range: 4 bpm for HR and 3% of the average pace or speed for movement (at least 5 s/km or 0.2 km/h), adjustable in the Suunto app from 2 to 9 bpm and from 1 to 10%. At an average pace of 6:00/km, 3% is 11 s/km. The movement range follows the reference average, so it can change by a second or two when the warm-up ends.
- Fixed scale: one level is exactly one steady range. Nine equally spaced vertical levels span 34–66% of the chart height. A point moves one level per full step in either direction and stops at the fourth: with a 4 bpm range, 0–3 bpm stays on the line, 4–7 bpm is one level, 16 bpm or more is the outermost level. Through 3.00 the farthest point stretched the scale, so a warm-up could hide smaller drift in the other points. Relative to the current drift, faster movement and higher HR are drawn higher; the live endpoint itself stays at 50%.
- Status labels: STABLE covers deltas smaller than the steady range. From the range upward, movement shows AHEAD or FADE and HR shows LOW or HIGH. During the warm-up both detail views show WARMUP instead; the app marks it in the zone field of the drift packet. Stable and warm-up values are white; AHEAD and LOW are green, FADE and HIGH red.
- Lines and dots: the green line is 8 px wide and the red line 6 px; both widths double when the canvas height exceeds 320 px. The red line is drawn on top. Endpoint radii match line widths. A standalone dot appears before the first line segment is available.
The coloured bar on the right edge is your current heart-rate zone, in
Suunto's standard zone colours. Zones 1–4 draw progressively longer bars;
zone 5 fills the available height. No bar is drawn without a valid zone.
The website demo uses synthetic data and the same chart rules. When the watch scrolls into view, its chart
starts as the current-drift dot and adds one historical point every
two seconds, then keeps looping. Ten demo seconds represent one history minute. The demo
joins the workout about 40 minutes in, after the default 10-minute warm-up, so it shows
the widest 16-8-4-2 groups from the start. Its reference averages
are fixed over the complete repeating scenario so each loop stays consistent;
the watch uses the live averages described above.
