Study of the projectional emittance is an efficient way of probing the quality of a particle beam. In this work we deal with some computational aspects of the problem. We present the argument that in a beam optic code for the design or evaluation of the performance of electrostatic extractors/accelerators which produce such (round) beams, one must include in the calculation beamlets with skew angles. This is necessary if one wants to compare calculations with emittance measurements for a beam with transverse temperature. We have developed new steps and modified an existing code for such a purpose and produced calculated results of emittance plots that can be compared with experimental observations.