The words this industry uses loosely

Ask three vendors what availability means and you will get three answers that agree in outline and differ where the money is. Time-based or production-based. Whether scheduled maintenance counts against it. Whether grid outages are excluded, and whether that exclusion also applies to a curtailment the grid operator requested. Each choice is defensible, and each moves the number by more than the effect most performance work is trying to find.

The same is true further down. Performance ratio, energy-based loss, lost production, and underperformance all appear in vendor material as though they were interchangeable, and they are not. A figure for lost production computed against a manufacturer's power curve and one computed against a machine's own historical expectation can differ by a factor of several, and neither is wrong - they answer different questions, and the material rarely says which.

This is why we publish a glossary and treat it as part of the product rather than as search engine surface. A written definition is the cheapest form of honesty available to a vendor, because it can be held against the product afterwards. If our definition of underperformance is on the site, a customer can check whether the findings match it, and any gap between the two becomes our problem rather than a matter of interpretation.

The test each definition has to pass is that a practitioner could read it, look it up elsewhere, and find our meaning rather than a meaning we invented for commercial convenience. Where the industry genuinely disagrees - and on availability it genuinely does - the entry says so and gives the alternatives, because a definition that resolves a real disagreement by picking a side and not mentioning the other one is a marketing document with a dictionary's formatting.

There is an argument that this is over-engineering a vocabulary problem, and that customers care about outcomes rather than definitions. In most industries that would be fair. In this one, the outcome IS a number, the number depends on a definition, and the definitions differ between the vendor producing the figure and the service agreement it will be discussed under. Precision here is not pedantry; it is the difference between two parties agreeing and two parties believing they agree.

The limit we accept is that a glossary cannot settle an industry. Nothing here binds anyone else, and a customer comparing two vendors will still be comparing two vocabularies. What it can do is make one of the two legible, which is enough to have a specific conversation instead of a general one.

The suggestion for any operator evaluating performance analytics, ours included: before looking at a single result, ask the vendor to write down what they mean by underperformance, what baseline it is measured against, and what is excluded from the calculation. The answer takes a paragraph, and the willingness to give it in writing is informative on its own.