Why does the number differ from the old Excel report?

If you put OPEREX’s monthly availability next to your previous Excel report, the numbers can differ — and that is not a bug, but the consequence of a deliberate, more accurate counting rule. This page shows what the difference is, when the two agree, and how to compare them.

The two rules

The difference comes down to a single question: which month owns an outage that spans the month boundary?

• The familiar Excel report books the entire duration of the outage to the month in which it started (the report groups by start date).
• OPEREX cuts the outage at the period boundary: each month gets exactly the part that actually falls into it.

Why cutting is the more accurate rule

Availability is a ratio: the share of the month’s hours during which the equipment ran. A ratio can only contain what actually falls into that month. Start-date accounting misleads in two ways:

• It charges the wrong month. The example above is real data: a 10-day outage started an hour and a half before the end of the month. Under the Excel rule all 240 hours burden June — although only an hour and a half of it happened in June — while July looks spotless even though the plant stood still for 10 days.
• It can produce impossible numbers. For a long outage spanning several months, the starting month gets more downtime hours than the month even has — “availability” then comes out as a negative percentage, which has no physical meaning. Meanwhile the months in between show 100% although the plant never ran.

The cut-based number always stays between 0% and 100%, and tells the truth about every month.

When the two agree

If no outage spans a month boundary, the two rules give the same number. The difference comes exclusively from boundary-spanning outages — the longer your outages, the larger it can get.

How to reconcile the two

If you want to put the OPEREX number next to the old report:

1. Open the month’s outages with the tile’s “Open source” link.
2. Take the outages that started in this month — regardless of their end date.
3. Add up their full durations: that is the Excel-style number. The OPEREX number counts, from the same outages, the part that falls into the month.

Compare layer against layer

Availability is layered: MA counts only mechanical outages, OSF counts all of them. When comparing two reports, first make sure you are looking at the same layer — next to the two boundary rules, this is the second most common source of a mismatch.

Related

Operations analytics overviewWhat the module is for: views, metrics, export, scheduled reports.