Figure 1.
Scheme for calibration by global reference and by working reference. (a) Signal from samples collected at one site (experimental, EA; local reference, C′A; global reference, CA) are on a different scale compared to those collected at another site (experimental, EB; local reference, C′B; global reference, CB). (b) To harmonize the signals, we set a common scale relative to the global reference material (CA and CB). While the signal may not be measured on the same absolute scale (1a), as long as these reference materials are the same sample they should represent the same quantity. (c) Signals measured for batch A and batch B are calibrated by reporting their signal relative to the reference material signal. In cases necessitating a local working reference material (C′), experimental samples can be calibrated to their respective local working reference and then secondarily calibrated to the global reference.