Do not treat metrology as an abstract term. It is part of daily life, and a trustworthy measurement environment is part of a harmonious society.
20 May is World Metrology Day. Ningbo quality-supervision experts explained several everyday measurement issues and urged attention to metrology around us.
A 55 L tank
Why can it take 60 L of petrol?
“My tank is only 55 L, but the dispenser showed 60 L — not counting fuel already in the tank. The dispenser must be wrong!” Mr Chen of Jiangdong called the 12365 hotline about a local station.
This “oddity” was not unique to Mr Chen
After the complaint, inspectors checked nozzle No. 2 and the other three dispensers. All four dispensers and nine nozzles were qualified; there was no short measure.
Expert comment:
Why can a 55 L tank take 60 L of petrol?
Experts said many drivers misjudge the nozzle with the wrong method.
“Since last year, 12365 received 12 complaints of short fuel measure; inspections were generally compliant. Citywide verification of 392 stations showed 96% of nozzles qualified; failures were mostly aged or overdue equipment, not proven fraud.”
Why are verified dispensers still complained about? Metrology Institute experts gave three reasons:
First, judging from the labelled tank capacity is wrong. The stated capacity already leaves 5–20% headspace for thermal expansion and excludes filler-neck and unusable bottom volume. That was Mr Chen’s mistake.
Second, judging fill quantity from the dashboard fuel gauge is unreliable. Most gauges use a float and sensor and only roughly indicate level. Fuel can overflow while the needle is not at full, or the car can stall while a bar remains — many drivers have seen this.
Third, judging from claimed L/100 km is unscientific. Congestion, load and driving style dominate fuel use; a “short fill” feeling often reflects road and vehicle conditions, not the dispenser.
What makes a dispenser qualified? Inspectors say “three checks”:
First, look for the mandatory-verification mark. Dispensers are nationally controlled measuring instruments, verified every six months plus random checks. A valid “mandatory verification” sticker (six-month validity) must be present.
Second, check that lead seals on the flow meter, sensor and main board are intact. Seals applied after verification stop reprogramming; a broken seal cannot be reused.
Third, before fuelling, check the display: except unit price, other indications should be zero.
The bureau also reminds consumers that if a fill seems short, they may ask for a 20 L standard metal measure (the “fair can”).
Why blood pressure was “raised”
as high as 180/120?
Mr Zhang’s 65-year-old mother has high blood pressure; he bought a home sphygmomanometer to adjust medication.
With family care, her blood pressure stayed around 120/80.
A few days earlier her reading suddenly rose to 180 / 120 or more.
Seeing the numbers, the elderly woman panicked and felt unwell. The family rushed her to hospital — a false alarm; her blood pressure was still stable.
How did blood pressure “rise” by itself?
Inspection found the home sphygmomanometer had leaked mercury, so readings were wrong.
Expert comment:
As health awareness grows, many homes have compact sphygmomanometers, but few have them checked regularly.
Typical home-sphygmomanometer faults: dust in the glass tube, leaks, broken mercury column, bubbles, low mercury, or a blocked inflation bulb that makes pumping hard.
These “small” faults easily skew readings. A leak raises pressure in the tube and under-reads; dust slows the mercury column; residual mercury below the tube also harms accuracy over time.
Most home sphygmomanometers are mercury types or aneroid gauges, which are accurate and easy to adjust. Do not pump too hard (mercury can leak); after use, tilt the unit right before closing the valve so mercury returns for the next reading.
Electronic sphygmomanometers cause the most complaints. Sensors can drift. Rest 10–15 minutes before measuring; avoid alcohol, smoking and strong tea; sit still with the cuff at heart level.
To protect patients, the bureau recently inspected sphygmomanometers, thermometers, X-ray, B-ultrasound and oxygen inhalers citywide.
City-level hospitals’ medical measuring instruments were in good condition; some township clinics and private practices were “sub-healthy”.
Among those “sub-healthy” instruments, sphygmomanometers were over 90% — the main problem.
Experts note that sphygmomanometers in the mandatory-verification scope carry an oval red mark with a validity date after they pass. Patients can check the clinic’s device this way.
A 0.6 kg fish
why only 0.4 kg?
Last Friday afternoon the reporter visited the street market north of Tongtu Road Primary School.
A stall sold crucian carp at 11 yuan/kg, 2 yuan cheaper than the market. The electronic scale showed 0.6 kg, 6.60 yuan.
“Experience says this fish is not 0.6 kg,” the reporter thought. The vendor insisted there was no mistake.
Still doubtful, the reporter bought the fish. At home it weighed only 0.4 kg — 0.2 kg short.
The reporter argued with the vendor, who denied it until onlookers gathered, then admitted the scale was “not very accurate” and refunded.
Afterwards the reporter took the fish along fruit and deli stalls; displayed weights still differed.
Expert comment:
Why is the “electronic scale” wrong?
City metrology experts listed these cases:
First, “added magnet”: a magnet under the platter increases indicated weight.
Second, “remote control”: a decoder is added in the circuit so a remote increases weight during sale.
Third, a hidden switch: on, the scale overweighs; off during inspections, it reads normally.
Besides these three methods, some stalls cheat electronic scales in other ways:
— Selling with the pan. The scale zeros empty, but the pan is weighed with the goods.
— Not zeroing. Previous weight is left on and added to the next item.
— Blocking the view. The display is hidden and a weight and price are called out at will.
— False unit price. The vendor raises the unit price while the display shows only weight, not unit price or total.
— Inertia shock. Goods are slammed onto the pan so the reading jumps, then lifted at once.
These scale cheats are most common at mobile stalls.
How should we deal with these cheats?
Metrology experts say the quickest check is the market’s fair scale. Markets in the three old urban districts have them; city verification found 100% of those scales qualified.
When weighing at markets, also note:
First, look for the “trusted scale” label — a mandatory-verification mark with a validity date on the electronic scale.
Second, the scale should show zero; tare packaging, especially heavy wrapping, at checkout.
