When a prove starts, the very first thing worth capturing is how the meter was performing before anyone changed anything. That value is the as-found meter factor, and it is the honest measure of what the meter was actually doing during the whole period since the last prove. The factor applied afterward, the as-left, is a separate number - and the gap between them is where measurement-bias and prior-period decisions come from.
As-Found Meter Factor in one line: The as-found meter factor is the factor that describes how the meter was performing at the start of a prove, before any adjustment, reflecting its behavior over the period just ended. The as-left factor is the value put into service afterward. Comparing as-found to the factor that was actually applied reveals any measurement bias and drives prior-period volume-correction decisions.
The as-found and as-left concepts come straight from calibration practice, where you record an instrument's reading before you touch it and again after you adjust it. Applied to custody metering, the as-found meter factor is what the current prove establishes for the meter in the condition it was in on arrival - the state it had been in, presumably, throughout the period since the last prove. It answers the question that actually matters for the volumes already measured: how was this meter really behaving while it was billing product?
The as-left factor is the value the meter is left running on after the prove, which is normally just the newly proved factor going forward. In a simple prove where nothing is physically adjusted, the as-found and the going-forward factor are the same measurement; the distinction becomes sharp when something is changed during the visit, such as cleaning the meter, replacing a part, or adjusting a flow computer setting. Then the as-found describes the old, unchanged condition and the as-left describes the new condition, and they can differ meaningfully.
Keeping the two labeled separately is what preserves the truth about the past. The as-left factor governs the future - it is what the meter runs on until the next prove. The as-found factor governs the interpretation of the past - it is the best evidence of what the meter was doing during the period that just closed. Collapsing them into a single number, or overwriting the as-found before it is recorded, destroys the information needed to judge whether the volumes already measured were biased and by how much.
The commercial reason as-found matters is measurement bias on volumes that have already been bought and sold. During the interval since the last prove, the meter was billing on some previously applied factor. The as-found factor from the current prove is the fresh, direct evidence of what the meter was truly doing over that same interval. If the as-found differs from the factor that was actually applied, then every volume measured in that interval was biased by roughly that difference, consistently in one direction. That is not random scatter; it is a systematic error with a sign and a size.
Whether and how to correct for that bias is the prior-period adjustment decision, and it hinges on the as-found value. A small difference within the meter's normal repeatability is usually accepted as noise and left alone. A large, clear difference means the volumes for the period were materially mismeasured, and the parties may need to compute a retroactive correction - a prior-period adjustment - to make the accounts right. The as-found factor, compared against the applied factor, is the number that quantifies the exposure and grounds that negotiation in evidence rather than argument.
This is why the discipline of capturing as-found before doing anything else is not bureaucratic caution but commercial necessity. If a technician cleans the meter or tweaks a setting before recording the as-found, the old condition is gone and can never be recovered, which means the bias on the closed period can no longer be measured. The rule is therefore firm: establish and record the as-found factor first, then make any adjustments, then record the as-left. That order protects the ability to reconstruct what really happened to the volumes already exchanged.
Because the whole value of the as-found factor depends on capturing it at the right moment and never losing it, the record-keeping is where this concept lives or dies. A cloud SCADA platform can log each prove with both its as-found and as-left factors distinctly, timestamped and tied to the specific meter, so the two are never conflated and the as-found is preserved exactly as measured. Merobix records these values alongside the meter's measurement history and makes them viewable from any browser, so the evidence for a prior-period discussion is retrievable long after the technician has left the site.
Having both values on record also lets the platform quantify the bias directly. By comparing the as-found factor against the factor that had actually been applied to the volumes since the last prove, the system can show the size and direction of any systematic error over that period, and can flag when that difference is large enough to warrant a prior-period-adjustment conversation. That takes the bias calculation out of a spreadsheet done after the fact and puts it next to the live data, where it is harder to miss and easier to defend.
As with the rest of the proving chain, the certified prover and flow computer produce the factors; the cloud SCADA does not compute or replace them. Its role is to capture the as-found and as-left distinctly, preserve them in an auditable trail, and surface the comparison that drives bias and prior-period decisions. This is the custody-metering counterpart to the general as-found and as-left idea from calibration, scoped specifically to the meter factor and to the commercial consequences of the volumes that were measured before the prove.
The as-found meter factor describes how the meter was performing at the start of a prove, before any adjustment, and so reflects its behavior over the period just ended. The as-left factor is the value the meter is put into service on afterward, governing the future. In a simple prove with no physical change the two coincide, but when the meter is cleaned, repaired, or reconfigured during the visit they can differ, and both should be recorded separately.
Because it is the direct evidence of what the meter was truly doing during the interval since the last prove, when volumes were being billed on the previously applied factor. If the as-found differs from that applied factor, every volume in the interval was systematically biased by roughly that difference. Comparing the two quantifies the exposure and is what drives any prior-period volume correction.
Because adjusting the meter first, by cleaning it or changing a setting, erases the old condition and makes it impossible to measure how the meter was behaving during the period that just closed. Once the as-found is lost, the bias on already-measured volumes can no longer be quantified. The firm rule is to establish and record the as-found factor first, then make adjustments, then record the as-left.
Safety & engineering notice. This article is general educational information, not site-specific engineering, safety, or legal advice, and it does not reflect any particular facility. Standards and regulations (for example OSHA, API, IEC, ISO, NFPA, NIST, and NERC CIP requirements) change and vary by edition, jurisdiction, and application. SCADA and remote monitoring cannot verify physical isolation, atmosphere, lockout/tagout, permit status, or a safe go/no-go decision. Qualified personnel must perform site-specific engineering, hazard analysis, and safety review, and confirm current requirements with the authority having jurisdiction, before acting.
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