In the first part of the article, the difference between the performance parameters precision and accuracy and its significance was explained. The second part takes a closer look at these two performance indicators.

Three possible subsets of a data set including L × M × N measurements:

1) One dispensing channel dispenses a run of N aliquots for the intra-run experiments.

2) One dispensing channel dispenses M runs of N individual volumes of liquid per run for the evaluation of inter-run performance.

3) L dispensing channels dispense one run each of N individual liquid volumes for tip-to-tip experiments.

The characterisation of the dispensing performance within the four levels (1) intra-run, (2) inter-run, (3) tip-to-tip and (4) load-to-load performance enables a systematic, detailed and above all differentiated analysis of precision, accuracy and possible sources of error. (1) Intra-run measurements primarily provide information about the basic precision and accuracy of a single dispensing channel of a liquid handler that dispenses aliquots in a continuous run. Errors incorporated by pause times or using different tips are excluded from this analysis. (2) Inter-run measurements reveal errors due to pause time effects and evaluate the reproducibility or stability of a system. The delay time between any two runs for the purpose of characterisation can be adjusted to the anticipated pause times of the respective application, ranging from a few seconds to hours or days. (3) Tip-to-tip measurements evaluate error sources due to variations in the dispensing channel (e.g. different cartridges, nozzle variations, tubing variances, different pressure levels for different dispensing channels, etc.). (4) Load-to-load measurements assess sources of error due to loading operations using, for example, a cartridge or a disposable tip.