How to read APL calibration certificates
Reading and interpretting calibration results correctly is vital. International efforts to support the International System of Units (SI) is a great example of global cooperation for a common goal. However, not all calibration reports present data in the same way or use the same terminology. The below information will help ensure that you interpret our reports as intended. If anything remains unclear, please feel free to contact us.
80k+
Instruments Calibrated
2000+
Customers Serviced
30+
Years Accredited
Glossary of Terms in APL Cerificates
Corrections: This is the quantity to add the instruments reading or output to determine the true/expected value, to compensate (“correct”) for any errors that we have observed in the instrument performance. Some laboratories quantify the error observed in your instruments, but we prefer to state the correction that you need to apply at each point. The correction and error are typically the same size but opposite direction from each other (correction = -1 x error).
As Found Readings: The performance of the instrument before any adjustments have been performed, i.e. the performance of the instrument as it was received by APL. These can also be called “before adjustment” readings. Where no adjustment has been performed, “not adjusted” will be shown in this column.
Uncertainty: All APL reports include an uncertainty value expressed at each calibration point. This is the band within which we are confident that the corrections (or errors) reported for your instrument are true, with 95% confidence. This includes many components, such as how well we know the true applied quantities from our reference equipment (i.e. the uncertainty inherent in our reference equipment and environmental factors) as well as the resolution and repeatability of your instrument during the test. In general terms, this is a measure of the quality of the correction, or how sure we are about the correction and readings that we have reported for your instrument compared to the true quanties.
Reference Level (for pressure): Due to the pressure induced by the weight fluids under gravity (manometric principle) where pressure is proportional to the height of the fluid above a datum, it is critical to define the datum from which we have performed the calibration of your instruments. The datum on your instrument that we adopt during calibration is described on your report as the reference level. This is either a location specified by the manufacturer or another fixed feature near the sensor location on your instrument that we can refer to.
Recommended reading
Some metrology concepts and terminology can be confusing or unfamiliar for even highly skilled and technical instrument users. There are many useful resources that help explain how laboratories agree on terminology, estimating uncertainty and determining compliance. These include: