Currently the power, HR and cadence all share the same Y axis, the limits of which are set automatically. As a result, people with low FTP can read their HR well in the graph, while people with higher FTP are left with very little resolution in the Y-direction.
I pulled up some random Mills workouts from different users, using the “all rides” functionality:
Note that the second person can more easily see the HR variation.
My proposal would be to:
add a HR/Cadence 2x checkbox
This changes the legend labels in the top: Heart rate -> Heart rate (2x)
HR and cadence (red & white) curve are multiplied by 2 -> pane with details on mouseover still gives the actual (unscaled) numbers of course.
make the default setting for the checkbox a profile setting. Anyone with FTP > 250W probably always wants this turned on.
To me it seems natural to use the available space in the Y-direction for showing the results. Now the HR and cadence data is so squeezed in a tight vertical space, simply because HR will generally be between 100-200, while our power can spike much more. Would be great to see HR changes more clearly!
ps: a more general possibility would be to allow the user to 1) set the min/max Y-limits, 2) adding a right Y-axis (again with min/max edit box), 3) being able to assign properties to each axis (e.g. assign only HR to right Y-axis and set Y-axis limits for HR). You could still write an algo to automatically reuse the current horizontal grid lines for left and right axis. This would give more freedom but it is clearly a bridge too far. The suggestion I made above seems to me to be the “80% of the results for 20% of the effort” option.