Reference
Reference
Terms, in plain English
Our own explanations. The formal definitions are in the free JCGM 200 (VIM).
- Traceability
- An unbroken, documented chain of calibrations linking a measurement back to SI units, each link carrying its own stated uncertainty.
- Measurement uncertainty
- A number describing how far the true value could reasonably be from the reported one. It travels with the result; a result without it is incomplete.
- TUR (test uncertainty ratio)
- The tolerance of the device being calibrated divided by the expanded uncertainty of the calibration. Bigger is better; 4:1 is the traditional target.
- Guard band
- A margin pulled in from the tolerance limit so that a pass/fail call accounts for measurement uncertainty and keeps the risk of a wrong call low.
- Decision rule
- The stated rule a lab uses to call a result in or out of tolerance, including how uncertainty is taken into account.
- As found / as left
- Readings taken before any adjustment (as found) and after (as left). As-found data shows how the instrument behaved in service.
- CMC (calibration and measurement capability)
- The smallest uncertainty an accredited lab can achieve for a given measurement under normal conditions, as listed on its scope.
- Reference junction
- The thermocouple junction held at a known temperature (0 °C in the reference tables). Real instruments compensate for it electronically.
Pt385 Callendar–Van Dusen coefficients
| A | 0.0039083 |
|---|---|
| B | -5.775e-7 |
| C (t < 0 °C only) | -4.183e-12 |
Pressure factors (Pa per unit)
| Unit | Pa |
|---|---|
| pascal (Pa) | 1 |
| kilopascal (kPa) | 1000 |
| megapascal (MPa) | 1000000 |
| bar | 100000 |
| millibar (mbar) | 100 |
| pound-force per square inch (psi) | 6894.757293168361 |
| standard atmosphere (atm) | 101325 |
| torr | 133.32236842105263 |
| millimetre of mercury, conventional (mmHg) | 133.322387415 |
| inch of mercury, conventional (inHg) | 3386.3886403409997 |
| inch of water, conventional (inH₂O) | 249.08890999999997 |
| millimetre of water, conventional (mmH₂O) | 9.80665 |
| kilogram-force per square centimetre (kgf/cm²) | 98066.49999999999 |
Torque factors (N·m per unit)
| Unit | N·m |
|---|---|
| newton metre (N·m) | 1 |
| centinewton metre (cN·m) | 0.01 |
| decinewton metre (dN·m) | 0.1 |
| kilonewton metre (kN·m) | 1000 |
| pound-force foot (ft·lbf) | 1.3558179483314003 |
| pound-force inch (in·lbf) | 0.11298482902761668 |
| ounce-force inch (in·ozf) | 0.007061551814226043 |
| kilogram-force metre (kgf·m) | 9.80665 |
| kilogram-force centimetre (kgf·cm) | 0.0980665 |
Factors computed from SI definitions (NIST SP 811). Thermocouple reference tables come straight from NIST’s ITS-90 database.