Before revision:   By integrating the results of our 1D and 2D touch-pointing experiments and reanalyses of previous studies' data, we examined the advantages and disadvantages of each approach to compute sigma_a, and we found that there is no optimal choice to maximize the prediction accuracy of FFitts law .
After revision:  By integrating the results of our 1D and 2D touch-pointing experiments and reanalyses of previous studies' data, we examined the advantages and disadvantages of each approach to compute sigma_a, and we found that using the parameter optimization method has overall the best prediction performance .