A fitted pressure curve should persist as a user setting, not reset every time

What it is

Once someone has set dead zone, slope, and saturation for their habit force band, that curve is a user setting. It should be written to disk with the account or device profile and read back on the next launch. Returning to the factory curve on every app open, document switch, or version bump forces people to fight the unfit mean curve again. Fitting pays off the second time the app opens; how calibration is sampled is a further step.

Why it happens

The parameters are small (a few knots or a gamma) but expensive to form: several trial strokes, visual comparison, maybe a calibration pass. If they live only in the current process, the cost is paid every time, and the rational choice is not to tune—so the product “has an adjustable curve” only for the first session’s novelty. The storage key must bind to the right entity. Binding to an install loses the curve on reinstall; binding to a document gives the same person two feels in two notes; binding to a pen serial puts A’s curve on B’s hand when the pen is shared. Stabler is the user account, with an optional override per pen model (a harder nib shifts the band). Migrate old keys on app update; do not silently cover them with a new factory curve. Live dragging in a preview should not write until confirm, or trial edits pollute the long-term profile.

Studying it

After calibration or manual edit, have people draw the same target thicknesses across a cold start, a simulated upgrade, and a document switch. Compare whether parameters remain and whether people notice a reset.

Independent variables: storage key (process / document / device / account), whether upgrades migrate, presence of “restore factory”. Dependent measures: whether the curve restores after launch, retune count, “I have to set it again”.

Check separately that the settings page shows last time’s values and that inking actually uses those values, so UI and runtime cannot drift apart.

Where it stops holding

On a shared, unsigned-in device (showroom, classroom), persisting to the machine leaves the previous person’s too-soft curve for the next; offer an explicit guest profile or reset at end of session. Cloud-syncing a force curve onto another device with a different sensor range may not fit; offset per device rather than refuse persistence. Developer debug switches should not be stored as the user curve.

Applying it

• Write the curve into user config so it survives cold start, document switch, and minor updates. Offer explicit “restore defaults”; do not treat launch as restore.
• Write on confirm; the value shown on the settings page must be the value the ink is using.
• Use a session profile on shared devices and return to factory on leave, so a personal curve does not stay on a classroom tablet.
• How to check: set a clearly too-soft curve, kill the process, reopen; a hairline should still go bold on a touch. Repeat after a simulated upgrade. Switching documents must not change the curve. Only “restore defaults” returns to factory.

Related

• Same group: C5.09.1 Natural grip force varies; the same curve is too soft or too hard · C5.09.3 Calibration samples a few force levels · C5.09.4 Unshared parameters force retuning in every app
• Adjacent: C5.01 Pressure Sensitivity · C5.17 Pen Pairing, Battery, and Loss
• Search: pressure profile · persisted settings · per-user calibration