What the numbers mean

Every figure this tool reports has a definition that can be got wrong, and several of them are wrong in a flattering direction — which is the dangerous kind, because nobody questions a number that looks good.

Empty is not zero

The rule the rest of the tool is built on.

A missing measurement is recorded as absent, never as zero. A NULL token count means the agent does not report tokens. A blank latency panel means nothing measured it. Neither means the work was free or instantaneous.

The distinction matters because zero is a value. Averaged, charted or summed, it makes a claim: that an agent cost nothing, that a session took no time, that no AI was involved. Absence makes no claim at all, which is the honest position when nothing was observed.

This is why status=undetermined exists instead of a "no AI" value, why Antigravity is excluded from cost panels rather than shown at 0, and why model= is omitted rather than emitted as unknown.

Cost is in tokens, never currency

There is no dollar figure anywhere in this tool, and that is a decision rather than a gap.

Under a subscription the marginal cost of a token is zero. Someone on a fixed monthly plan spends the same whether a session burns 10k tokens or 10M. Multiplying their token count by an API rate would report money nobody spent — not an imprecise figure, a categorically wrong one.

Nothing in any transcript says which billing model a user is on, so a currency figure would require guessing at the pricing model before even reaching the price. Prices also vary by contract and tier, change without notice, and differ across the four token classes.

Tokens in and out, per model, per branch, are exact and need no assumption. Anyone who needs money has their own contract and can multiply correctly for their own billing.

Cache writes count as uncached

The cache read ratio is:

cache_read / (uncached_input + cache_write + cache_read)

Cache writes belong in the denominator. A write arrives uncached and is billed above base rate — roughly 1.25x. Leaving it out turns a real 48% into a flattering 99%.

Measured on this project's own data, that error is not hypothetical: the first version of the analysis reported a 99% hit rate and concluded caching needed no attention. Recomputed with writes included, the real figure was 47.6%.

A panel reporting 99% recommends nothing. The flattering error is also the one that makes the dashboard useless.

Write payback breaks even at 1.25x, not 1.0x

Write amortisation is cache_read / cache_write — how many reads a write earned before expiring.

A write costs about 1.25x base and a read about 0.1x, so a write needs roughly 1.25 reads to pay for itself. A series sitting at 1.10x lost money while looking fine against a 1.0 line.

The dashboards draw break-even at 1.25 for exactly this reason, and use a log axis, because the measured spread runs from 0.73x to 21x — on a linear axis every sub-break-even series collapses onto the floor, which is the end of the range the panel exists to surface.

Report it per model, never as one number. Measured here, the aggregate was a healthy 3.60x while one model sat at 0.73x — a loss, invisible in the total.

The productivity section reports a difference, not a gain

The delivery dashboard compares assisted against unassisted commits. It reports a change-size difference and refuses to call it a productivity gain.

The reason is selection bias, and it is not resolvable by better maths: people reach for an agent on some kinds of work and not others. A throughput difference between the two groups may be measuring which work was chosen rather than what the agent did.

Every such panel carries its denominators and its n. Where a cohort falls below 20 commits either side, the figure is rendered as unavailable rather than as a number — a rate over a handful of commits moves several points on one or two of them.

Coverage is not adoption

Coverage is the share of commits carrying a valid trailer of any kind, including undetermined. A repository at 100% coverage may have had no agent involvement whatsoever.

Adoption is the share carrying status=assisted.

They are different questions and the first is often mistaken for the second. Coverage says the instrumentation is working; adoption says the agents are being used.

A fix rate is not a defect rate

The rework panel compares how often assisted and unassisted commits are fixes. purpose is classified from Conventional Commit prefixes and path heuristics, so it measures what commits were labelled, not what actually broke.

It is a rework proxy. Useful, and not the same thing.