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
Section titled “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.
A real example, with the numbers
Section titled “A real example, with the numbers”This is a DCPI plant’s June–July 2026 case (real data). The outage started on 30 June, ~1.4 hours before the end of the month, and lasted 10 days — until 10 July — for a total of 240 hours. June has 30 days = 720 hours, July has 31 days = 744 hours. Here is what each rule says about MONTHLY availability:
| Month | Old Excel rule (start month gets it all) |
OPEREX (cut at the boundary) |
|---|---|---|
| June | 66.7% — the full 240 hours land on June | 99.8% — only June’s ~1.4 hours |
| July | 100% — “spotless” | 67.9% — the outage’s ~238.6 hours |
Check it yourself: availability = (hours in the month − downtime hours) / hours in the month. Under Excel,
June is (720 − 240) / 720 = 66.7% and July is (744 − 0) / 744 = 100%. Under OPEREX, June is
(720 − 1.4) / 720 = 99.8% and July is (744 − 238.6) / 744 = 67.9%.
The Excel rule says June was the bad month and July was flawless — but it happened the other way round: the plant spent almost the entire outage in July. The OPEREX number tells the truth about both months: June was fine, July dropped. The same 240 hours — just booked where they belong.
Why cutting is the more accurate rule
Section titled “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
Section titled “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
Section titled “How to reconcile the two”If you want to put the OPEREX number next to the old report:
- Open the month’s outages with the tile’s “Open source” link.
- Take the outages that started in this month — regardless of their end date.
- 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.