1. A method of calculating an initial amount of a target nucleic acid N 0 in a sample, the method comprising: (A) receiving a first plurality of fluorescent measurements, wherein each respective fluorescent measurement FS n in the first plurality of fluorescent measurements is a fluorescent measurement taken in a different cycle n in a first PCR amplification experiment of the sample; (B) computing a first model that calculates the initial amount of the target nucleic acid N 0 in the first PCR amplification experiment, wherein, for each respective fluorescent measurement in the first plurality of fluorescent measurements, the first model comprises a respective equation for N n , wherein (i) N n is the calculated amount of the target nucleic acid in cycle n of the first PCR amplification experiment from which the respective fluorescent measurement was taken, and (ii) the respective equation for N n is expressed only in terms of K and N 0 , regardless of the cycle n of the first PCR amplification experiment, wherein K is the Michaelis-Menten constant for the first PCR amplification experiment, wherein the first model comprises an equation for N 1 , the calculated amount of the target nucleic acid in cycle 1 of the first PCR amplification experiment, wherein N 1 = N 0 ⁡ ( 1 + K K + N 0 ) ; and (C) calculating the initial amount of the target nucleic acid N 0 in the first PCR amplification experiment, using the first model.