It is critical to distinguish between the specifications for all 280-DS units and that of individual calibration of a single instrument.
The accuracy of the 280-DS is established by making multiple measurements with multiple units over multiple days, and then determining the average and standard deviation of these measurements using statistical means. The final accuracy is expressed as a +/- deviation value from the expected value. This value is documented on the 280-DS Specification Sheet.
Calibration is performed on a single 280-DS. Calibration ensures that the device measures up to or within the +/- accuracy value published for each parameter. On a calibration certificate, this is documented as the expected tolerance since it represents the criteria which a pass or fail result will be determined. The recorded number is not representative of the entire population of 280-DS units, but is representative of the readings taken by a single 280-DS at an instant in time. For this, the word Tolerance is more appropriate. Tolerances are chosen to be better than or equal to the accuracy of the 280-DS family specification. Tolerances are therefore derived from the accuracy specification for the 280-DS family.