Using effective target width in Fitts? law has been a widespread applied method for one dimensional pointing task evaluation especially when different speed or accuracy inclination exists. However, the concrete calculation methods of effective target width have not been offcially united. This paper concentrates on resolving this problem. Two special designed and controled experiments were described in this paper. The experiment and data analysis results show that after comparing the two existing methods of calculating effective target width, the method of mapping all the abscissa data into one united relative coordinate system to do the calculation is tested as better for human computer interface modeling than dividing data into two groups according to the corresponding target sides and mapping them into two separate coordinate systems.