Every crack grows on the same curve, and the curve has three regions. Engineers learn them the first week. Hindsight Daily already draws the curve from your record — this page names the regions in plain words, reads them as a life, and specifies the gauge that will tell you which one you are standing in.
Put a cracked piece of metal under a load that cycles — up, down, up, down — and measure two things: how hard each cycle hits the tip of the crack (engineers call this ΔK, the stress-intensity range), and how much the crack grows per cycle. Plot one against the other, both on logarithmic axes, and you get the shape below. The numbers depend on the metal; the shape does not. Aluminum, steel, titanium — same three regions.
Both axes are logarithmic — each step along them is a multiplying step, not an adding one. Left of the threshold the crack does not move. In the middle the curve is a straight line, which on these axes means a power law: growth rate rises as a fixed power of the hit. Past the onset of instability the curve bends upward and runs toward a vertical line — the fracture toughness of the material — where a vanishingly small extra hit produces unbounded growth.
Before the regions, the two axes — because the whole metaphor lives in them. Across the bottom is how hard each cycle hits the flaw. Not how heavy the week was in total; how hard each single load landed on the one place you are cracked. Engineers write it ΔK, and it grows with two things: the size of the load swing, and the size of the crack it lands on. A small argument on a big old wound is a big hit. A big argument on nothing is not. Up the side is how much the flaw grows per cycle — the damage each day actually does. That is the number Hindsight Daily estimates from your nightly entry.
So the chart asks one question of any day: given where I am already cracked, how hard did today hit it, and how much did it grow? Everything below is what the three answers look like.
The cycles are real, but each one hits the crack too lightly to move it. This is not "no load" — you can be busy, tired, spending damage units all day — it is load that stays under the line where the flaw advances. An aircraft can live here indefinitely. So can a person.
In a life: the long stretch where the hard things are the right hard things — the mission your material was built for. A brutal training block, a big deliverable, a newborn: heavy, and yet the old wound does not open, because none of it lands there. The founder's card labels this region safe life, meaning a flaw that never moves — not the fleet philosophy of the same name in Lab Note 001. Region I is what the Mind My Material match is trying to buy you: a mission whose loads miss your crack.
The crack is moving, and the rate is knowable. This is the region the whole damage-tolerance philosophy is built for: you can calculate the growth, set an inspection interval, and fly on with a known flaw under a known limit. Most of a well-run life is spent here. The card's word is durability — and the thing to watch for is widespread damage, many small cracks at once.
In a life: the job that wears you a little every week in a way you can name. The relationship with one recurring fight. The commute. You are not fine, and you are not in danger; you are on a curve you can read, which is the best position a person with a known flaw can hold. The move here is not to fix it tonight. It is to keep the interval — the weekly review, the nightly number — so that the day the slope changes, you see it. The widespread-damage warning has a life shape too: not one big crack but six small ones (sleep, money, a friend gone quiet, a skipped run, a bill, a slight) that add up to the same margin loss as one big one, and hide better.
Past the onset of instability, a little more load produces a lot more growth, and then a lot more, until the curve runs into the vertical line: fracture. There is no interval short enough to catch it. The engineering term is a rogue flaw. The point of the gauge is not to describe Region III. It is to show you the distance to it while you still have some.
In a life: the resignation email sent at 2 a.m. The sentence you cannot take back. The relapse. The week where every ordinary hit — a comment, a bill, a phone call — produced a reaction out of all proportion to its size, because the crack was already long and every load was landing on the tip. That is what "exponential" means in a life: the same day costs more than it did last month, and the cost is rising faster than the loads are. The founder's card was written from inside this region — I almost quit multiple times — and the honest instruction on it is the whole reason the gauge exists: know the margin before the unstable reaction, not after.
The chart is not a verdict, because both axes can be moved, and the cards say how. Shrink the hit. The 18 March card says it plainly: if you limit the stress amplitude and cycle, you could last indefinitely; carry the load in broken-up repetitions and sets. Same total work, smaller swings, lower ΔK. Give the corner a radius. The stress-flow exercise shows that the same load through a gradual change concentrates a fraction of what it does through a sudden one; the transitions in a life — a boundary, a move, a conversation — can be given a radius on purpose. Shorten the crack. A repair that actually works (the Repair Bay keeps the list) reduces the size of the flaw the next load lands on, and ΔK falls with it. Empty the residual stress. The Cycle of i page explains why the load locked in from before — shame, fear — makes every new cycle cost more; releasing it at −1 is the one move that lowers the whole curve.
None of these moves the fracture line. That is the material's, and it is where it is. All four move you — left, toward the region where the same life can be flown indefinitely.
The Daily already computes a damage index and its rate from your nightly number, and the crack-growth view already existed. Since v4.4.0 the Trends panel carries one more tile beside the inspection date: CRACK-GROWTH REGION. It reads the same crack-growth track the structure view draws, and it says Region I, II, or III with one interpreting phrase, in the same style as every other tile on the panel. Tap What does this mean? under it and it explains itself.
| Tile shows | Interpreting phrase | What the pilot does |
|---|---|---|
| REGION I | "Below threshold. The load is real; the flaw is not moving." | Nothing required. This is what a mission-matched material looks like at cruise. |
| REGION II | "Controlled growth. Inspection interval holds." | Keep the record. Keep the interval. Read the trend, not the day. |
| REGION II ▲ | "Growth rate climbing. Margin to Region III is shrinking." | The one flag on the panel that earns a look at the envelope today, not next inspection. |
| REGION III | "Unstable. This is not a trend read; it is a ground call." | Stop reading gauges. The right instrument is a person. |
How the lines are drawn, in this release: every threshold is self-referenced to your own record, the way every other Track-B quantity in the Daily is. Region I is the inspection gauge's own "quiet" test — at your trailing-90-day rate the crack index would take more than 180 days to grow 10%. Region II ▲ means the last 30 days are growing it at least 1.5× as fast as the trailing 90. Region III is the same condition the structure view already calls "time for a real repair" — the index at or past your critical size — and it needs a calibrated record (an anchor date), because without one the level of the index is arbitrary and the tile says so. Re-anchoring the thresholds to the reference record (the 2,395-day founder dataset) is proposed on this page and not yet built; when it is, the tile will say which it is using.
Aircraft engineers never state a life without saying what evidence it rests on, and they make the bill explicit: the less evidence, the bigger the safety multiplier they divide the answer by. They call that multiplier a scatter factor. The lab uses the same idea, with medal names so that nobody needs the vocabulary.
| Tier | In the hangar | In the Daily | What it means for the reading |
|---|---|---|---|
| Bronze | Analysis only — no test article. Scatter factor 7–8. | 13 to 89 days of record (the trial) | A provisional read. Direction is useful; numbers are not yet. |
| Silver | Coupon tests — small samples of the real material. Scatter factor 5–7. | 90 days to one full block | Trend and region are trustworthy, on your own record's thresholds. |
| Gold | Full-scale test — the whole structure, to failure. Scatter factor 3–4. | A completed block with a recertification | Your own thresholds, your own curve, checked against a finished block. The reading is yours. |
In the Daily the tier rides in the tile's tag line — BRONZE READ · 19 DAYS, then SILVER READ · 90+ DAYS — so the medal is never separated from the number it qualifies. Gold is the program's word, not the app's: the app cannot see a recertification, so it never claims one. Known knowns, known unknowns, unknown unknowns — same ladder, different words. A gold reading is not a better life. It is a better-known one.
It cannot see why the load is what it is. It cannot tell a hard week on a good mission from a hard week on the wrong one — the alignment map exists for that. It is sequence-blind in the ways the framework already admits. And it will never draw the curve out to failure or count down to anything. Spent is knowable; remaining is not.