Main objective of this lecture is to present on Determining the Number of Wavelengths. It is a tutorial based lecture. Wavelength is defined as the distance between two nearest points of the adjacent c crest or trough. The number of wavelengths required for consistent simulation seems to depend on the size of the raindrop, with many wavelengths being needed for small drops. As the computation time decreases for smaller drops, it is possible to increase the number of wavelengths used for small drops without incurring a dramatic penalty in computation time.