Lightning is a captivating natural phenomenon but indisputably terrifying. Therefore, lightning studies have played an essential role in establishing safety regulations to protect lives and infrastructures. Among the many simulating functions that were utilized in the past for modelling the lightning return-stroke current, Heidler and Pulse functions overcame certain limitations, including the time derivative discontinuities. Incompletely-recorded current derivative signals represent another challenge in lightning research. This thesis proposes a double-term Pulse function that could be investigated with the double-term Heidler function for modelling the lightning return-stroke current. The time derivative of both Pulse and Heidler functions have been used to simulate the current derivative signals recorded on June 10, 1996. Some of these return-stroke signals exceded the maximum set level. Consequently, the double-term simulating functions were used to recover a large incompletely recorded return-stroke current derivative signal. The R2 fitting factor was used to evaluate the quality of each fitting to determine which simulating function is better suited to model and recover valuable return-stroke current signals.