Skip to content

Reading OEE

How-to. What each segment of the OEE screen means and what to do about the grey one.

The OEE screen follows ISO 22400 in its arithmetic and house rule 2 in its honesty: a KPI that cannot be computed returns unknown and says why. That is the grey segment.

The segments

Segment Source Becomes unknown when
Availability machine state history from the tag map's state tag the MES was not subscribed for part of the window (it started later, the connection dropped, the machine went stale)
Performance counter deltas against the rated cycle time in the tag map the rated cycle time is blank, or a counter reset happened inside the window
Quality good and scrap counters there is no scrap counter in the tag map — quality reads unknown, not 100 %

The screen states its data source in a line under the number; a screenshot without that line is not a screenshot of this product.

Stale is not stopped

A machine whose tags stopped changing is stale, not down. Stale means the MES stopped hearing, which is a different fact from the machine stopping. Downtime is only booked from a state tag that says so; stale time is reported as stale and excluded from availability with a reason.

Unlabelled is reported as unlabelled

A downtime pareto that files unlabelled stops under "other" convinces a plant it has data it does not have. Here the unlabelled bar is named unlabelled. Reason codes are configuration; the how-to for shifts and reason codes is not written yet (as of 2026-09-07) — ask in Discussions and it moves up the list.

To shrink the grey segment

  1. Fill the rated cycle time for every machine in the worksheet.
  2. Give every machine a scrap counter, or accept that quality is unknown.
  3. Keep the agent running: the window it was not watching cannot be reconstructed later, by design.

See also