Measurement coverage

The share of inputs that were measured rather than estimated. Findings drawn from estimates are reported with lower confidence.

Formula

In practice

Measurement coverage is the share of the map's inputs backed by an observation, a system record or an engineered standard rather than by an estimate. The editor records the source on each input and can additionally hold sample size, measurement date, who measured it and an evidence note. The reason it exists in a calculation tool: two maps can report the same lead time to three decimals while one came from time studies and the other from recollection, and nothing else on the screen tells them apart.

It is not decoration. On a map below the threshold every finding's confidence is downgraded one step — except the two findings that are about data quality, which would otherwise argue themselves down and disappear at exactly the moment they were most warranted.

How this is calculated

The engine's reconstructed Acme Stamping current-state benchmark matches three published totals from Rother & Shook, Learning to See:

It also matches the example's central finding — assembly 1 at 62 s cannot meet a 60 s takt — and declines to report OEE, because the book's "uptime 85%" is not the three-factor measurement OEE requires.

Provenance. The fixture was reconstructed from the book's published totals rather than transcribed from a copy in hand, which made the benchmark circular: inputs chosen to reproduce an output cannot independently confirm that output.

On 2026-07-30 the reconstruction was cross-checked field by field against three independent teaching reproductions of the same current-state map. Every figure is corroborated — the five cycle times (1 / 39 / 46 / 62 / 40 s), the five inventory quantities (4,600+2,400 · 1,100+600 · 1,600+850 · 1,200+640 · 2,700+1,440), five days of coils, 18,400 per month split 12,000 LH / 6,400 RH over 20 days, the one-hour stamping and ten-minute weld changeovers, and two eight-hour shifts with two ten-minute breaks each.

Two sources disagreed, and both disagreements fail on arithmetic rather than on authority: spot-weld times of 45 s and 50 s sum to 198 s, not the published 188 s; and repeating 1,600+850 after assembly 1 gives 24.28 days, not 23.6. The corroborated set is the only one consistent with the published totals.

The sources also publish uptimes (85 % stamping, 100 % weld 1, 80 % weld 2, 100 % both assemblies) as bare percentages, with no planned time, run time or ideal cycle time behind them. The model can now hold a bare percentage as a stated availability, so the omission is a choice rather than a limitation: the fixture still omits it, because putting it in would move the benchmark's capacity figures away from the published totals this fixture exists to reproduce. The engine still declines to report OEE for it.

Weld changeover frequency remains an assumption: the book states every-part-every-two-weeks for stamping only, and no reproduction supplies the weld figures. It affects capacity, not any asserted golden figure.

This is corroboration by secondary sources, not verification against Rother & Shook. The remaining gap is narrow but real, so the note stays.

This is an accepted limitation, not an open task. Closing it needs a copy of the book, which the project does not have; no further work in this repository can narrow the gap, and the claim made in the README is worded to the evidence that exists. Anyone with the book in hand can check the fixture field by field against the figures listed above — that is the whole of what remains, and it is recorded here rather than tracked as work in progress.

Sources consulted: Arrizabalagauriarte Consulting · MapMyOps · SlideShare VSM deck

Methodology — Verification

Common questions

What counts as measured?

An observation, a record from a system, or an engineered standard. An estimate is anything else, including a confident one from someone who knows the line well. The distinction is about where the number came from, not about how likely it is to be right.

What does low coverage actually change?

The findings stay, and their confidence drops a step, so a report cannot present a conclusion drawn from recollection with the same weight as one drawn from time studies. The two data-quality findings are exempt, because downgrading them would let a poorly measured map quiet the warning about itself.

This definition is the one the product itself shows, read from its interface catalogue at build time.

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