Two suppliers quote the same range. One of them can prove it; the other has a PDF. The difference shows up six months later, when the first batch arrives and nobody agrees what "conforming" means.
First article inspection is the moment that ambiguity gets closed. Most buyers have never seen one for a rangefinder, so here is what it should contain.
Why a sample test is not enough
A sample tells you one unit worked once. A first article tells you both sides agreed what the part is, which is what makes later disagreements mechanical instead of emotional. Once signed, a returned unit is compared against a document rather than argued about.
The twelve records
1. Identity. Serial number, firmware version, hardware revision, recorded against the drawing revision. Without the revision this document is worthless six months later.
2. Dimensional. Housing, mounting holes, optical window position — measured, with the instrument named.
3. Mass. Measured against the declared value, tolerance stated. Sounds trivial; it is the number that quietly breaks gimbal designs.
4. Optical axis. Boresight offset between transmit and receive axes relative to the mechanical datum, in mrad. For an integrated sight this is the number that decides whether the reticle and the beam agree at 2 km.
5. Range verification. Measured range against a stated target at a stated distance in stated visibility — with the reference instrument named. "16 km" alone is not a record.
6. Accuracy. Constant and proportional error, measured at three or more distances. A ±2 m figure with an unstated per-kilometre term is not a specification.
7. Repetition rate. Achieved rate in continuous mode, plus the missed-return count over a fixed number of shots. The second number is the one that predicts field behaviour.
8. Interface. Every command in the protocol document exercised once, replies recorded. This is where an integration either starts clean or starts with a two-week debug.
9. Power. Current draw at idle, single-shot and continuous, at both supply limits.
10. Environmental. Temperature cycling result, and whether the unit was operated at both extremes or merely stored there.
11. Sealing. IP test method and result — or an explicit statement that it was not performed. An omission stated is information; an omission hidden is a surprise.
12. Safety. Accessible emission measured at the aperture, with instrument and standard cited. Note this classifies that build, not your product.
What to do with it
- Make it a line item in the quotation, not a favour. If it cannot be priced, it cannot be delivered.
- Ask for it once, on the first article, and keep it. Later units are judged against it.
- If a supplier cannot produce one, that is a data point about how the next twelve months will go — not a reason to negotiate harder.
The twelve fields, as a checklist you can send directly, are here. The range test report template that pairs with it is here.
I keep an open dataset of 59 rangefinder and single-point lidar modules at specs.erdilrf.com — every range figure carrying the manufacturer's own test condition, plus interface and optics tables. JSON and CSV, CC BY 4.0, no signup.
If you have a first-article horror story — a dimension that was "measured" without an instrument, a firmware revision nobody wrote down — I would like to hear it. Those are the ones worth writing about.
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