Determination of the efficiency for the standard, reference and clinical samples. The threshold cycle is the cycle number at which the fluorescence curve for a given sample crosses the user-defined noise band. Log to the concentration for the reference samples is set as log to arbitrary numbers with four-fold difference as the reference samples are four-fold serial dilutions. The actual concentration is not needed when determining the efficiency as it depends on the slope of the line only.
Mygind et al. BMC Microbiology 2002 2:17 doi:10.1186/1471-2180-2-17