Name: Reserve Tank - W' Balance & Durability
Author: QNCC

Your anaerobic "tank" as a live fuel gauge — with a fatigue model no other data field has.

Reserve Tank shows your W' balance ("W prime"): the finite anaerobic energy you can spend above Critical Power. Every watt above CP drains the tank; riding below CP refills it (Skiba differential model). The big number is your remaining reserve in percent, and the bottom bar drains inward from both ends — glanceable at race pace.

WHAT MAKES IT DIFFERENT

• Durability model: your body at hour 4 is not the body that started the ride. Based on published research (Clark, Spragg, Mateo-March, Chorley), the tank shrinks, effective CP erodes, and recovery slows as work accumulates — you see the bar's outer ends darken as capacity is lost. Pick an Elite / Trained / Recreational preset, or turn it off for the classic model.

• Overdraw: the textbook model stops at zero — riders don't. Push past empty and a red bar grows outward from the center showing how deep in debt you are (negative %). Recovery pays the debt back before the tank refills.

• Surge counter: the field learns what your average attack costs this ride and shows "~N left" — how many more you can afford. Tick marks preview where the next surge will leave the bar.

• FIT recording: three developer channels (W' Balance kJ, W' Capacity kJ, Effective CP W), graphable in Garmin Connect after every ride — tune your settings against reality.

• Honest edge cases: power dropouts hold the last value 3 s, then flag the field (gray bar, "--") instead of silently refilling the tank; recovery keeps running through auto-pause; changing settings mid-ride preserves your balance.

• Optional tone alerts at 50% and at empty; optional number-only display (hide the bar).

SETUP — IMPORTANT

Requires a power meter. Set YOUR Critical Power (roughly FTP) and W' capacity in the field settings from the Connect IQ phone app — the display is only as honest as those two numbers. Derive them from ~3-min and ~12-min max efforts, or from intervals.icu, WKO, or Golden Cheetah.

SETTINGS

• Critical power (W) and W' capacity (J)
• Fatigue model: Off / Elite / Trained / Recreational
• Overdraw scale, surge threshold, alert tones, hide bar

Rider weight for the fatigue model comes from your Garmin user profile. English and Spanish included.