A signal interpolation method is described. The method includes: receiving an analog input signal; digitizing the analog input signal received, thereby obtaining a digitized input signal having samples; determining a crossing of the digitized input signal with respect to a threshold that was set; and interpolating a signal between at least two successive samples, wherein the signal interpolated has two signal portions each having a linear slope, and wherein one of the signal portions crosses the threshold. A measurement instrument is also described.