Electronic flow measurement does not just accumulate gas continuously; it slices that accumulation into neat periods so the records line up with how gas is bought, sold, and billed. The two boundaries that matter most are the top of each clock hour and the start of the contract day, and the flow computer is built to close its running totals precisely on those boundaries. That behaviour is what people mean by even-hour and contract-day processing. This guide explains how an EFM computer snaps its period closes to the even hour, rolls the daily total at the contract hour, and handles the partial hour that inevitably straddles a boundary so that every record maps cleanly onto the billing calendar.
Even-Hour Processing in one line: Even-hour processing is the way an electronic flow measurement computer closes its running accumulations exactly at the top of each clock hour and rolls the daily total at the contract hour, so that hourly and daily records align to how gas is billed. The computer timestamps each period at the even boundary rather than whenever a poll happens to arrive, and it apportions any flow that straddles a boundary to the correct side. The result is a set of hourly records that sum to the day and daily records that begin and end on the contract-day boundary.
A flow computer runs a fast internal loop, sampling its inputs and adding to volume many times a minute, but the records it keeps are period totals, and those periods have to end on defined, repeatable boundaries. Even-hour processing means the hourly period closes at the top of the clock hour, on the even hour, not at some arbitrary moment tied to when a host happened to poll the device. At that instant the computer freezes the hour's accumulated volume and energy, finalises the flow-weighted averages and flow time for the hour, writes the hourly record with a timestamp on the boundary, and immediately begins accumulating into the next hour.
Anchoring the close to the even hour is what makes hourly records from different devices, and from different days, directly comparable and additive. Every meter closes its ten o'clock hour at the same wall-clock instant, so the numbers can be lined up, summed across a station, and reconciled against a counterparty's records without arguing about where one hour ended and the next began. It also means the twenty-four hourly records within a day sum exactly to the daily total, because they tile the day without gaps or overlaps.
This is a scheduling discipline built into the computer rather than something the polling system imposes from outside. A host might read the device at ten past the hour, or five minutes late after a comms outage, but the record it retrieves still carries the even-hour timestamp and the totals as of that boundary, because the computer closed the period on its own clock. That separation between when a period closes and when it is read is central to EFM: the measurement record is authoritative and boundary-aligned regardless of the vagaries of collection.
The daily boundary is a level up from the hourly one. A gas day does not necessarily start at midnight; it begins at a contract-defined hour, and the flow computer is configured with that contract hour so it knows when to roll the day. Contract-day processing means that at the contract hour the computer closes the daily accumulation, writes the daily record for the day just ended, and starts a fresh daily total. Because the contract hour is itself an even hour, the daily roll coincides with an hourly close, and the last hourly record of the gas day and the daily record share the same boundary.
Aligning the daily roll to the contract hour is what lets the measurement records feed billing directly. The invoice is written against gas days, so a daily total that begins and ends on the contract-day boundary can be dropped straight into the settlement without re-slicing. If the computer rolled at midnight while the contract ran a different gas day, someone would have to reconstruct each contract day by hand from hourly pieces, which is exactly the error-prone reconciliation that boundary-aligned processing exists to eliminate.
The relationship between the hourly and daily closes is nested and self-consistent. The hourly records within a gas day sum to that day's daily record, and successive daily records tile the calendar of gas days without overlap. Change the contract hour, and both the daily boundary and which hourly records belong to which gas day shift together, because the computer treats the contract hour as the single anchor from which the day is measured. Keeping that configuration correct is fundamental, since a mismatched contract hour quietly misassigns a slice of every day's gas to the wrong side of the billing boundary.
Real operations do not always start and stop on the hour, so partial periods are unavoidable, and the way the computer handles them decides whether the records stay clean. When flow begins or ends part way through an hour, that flow is accumulated into the hour it actually occurred in and closed at the next even boundary, so the partial hour is a genuine short record rather than a smeared one. The same applies at the daily level: gas flowing right up to the contract hour lands in the day that is ending, and gas after it lands in the new day, with the roll drawing the line exactly at the boundary.
Because every close is timestamped to a boundary, the accuracy of the flow computer's own clock is part of the measurement. If the device clock drifts, its even-hour closes land at the wrong wall-clock instant and its records no longer align with a counterparty's, which is why time synchronisation and any clock adjustment are treated as measurement-relevant events to be logged. A clock change large enough to move a period boundary is not a housekeeping detail; it can shift gas between hours or between gas days, so EFM records the adjustment rather than applying it silently.
For an operator running many metering points, a cloud SCADA such as Merobix makes the boundary discipline observable across the fleet. It collects the boundary-aligned hourly and daily records from each flow computer and presents them on the same gas-day calendar, so the twenty-four hours that should sum to a day can be checked, a device whose clock has drifted stands out against its peers, and a missing or duplicated period boundary is visible rather than buried. Because the records are already closed on the even hour and rolled at the contract hour by the computer, the platform's job is to gather, align, and surface them, giving the operator a clean, billing-ready view without re-slicing the raw accumulation by hand.
No. The flow computer closes each hourly period on its own clock at the top of the hour and timestamps the record to that boundary, independent of when a host polls it. If a poll arrives late or after a comms outage, the retrieved record still carries the even-hour timestamp and the totals as of that boundary. That separation between closing a period and reading it is what keeps the measurement record authoritative regardless of collection timing.
Because gas is bought, sold, and billed against gas days that begin at a contract-defined hour, which is often not midnight. The flow computer is configured with that contract hour and closes the daily accumulation there so the daily record maps directly onto the billing calendar. Rolling at midnight while the contract runs a different gas day would force someone to reconstruct each contract day by hand from hourly pieces.
The flow is accumulated into the period in which it actually occurred and closed at the next even boundary, so a partial hour becomes a genuine short record rather than being smeared across two periods. At the daily level, gas flowing right up to the contract hour lands in the day that is ending and gas after it lands in the new day. This keeps hourly records summing exactly to the day and daily records tiling the gas-day calendar without gaps or overlaps.
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