ReadGT3XPlus            Read the raw tri-axial accelerometry data csv
                        file by ActiGraph GT3X+.
ReadTable               Read the raw tri-axial accelerometry data csv
                        file.
Sigma0                  \bar{sigma}_i computing using raw accelerometry
                        data
TimeScale               Time scale vector from 00:00:00 to 23:59:59.
computeActivityIndex    Compute Activity Index
print.ActivityIndex     Print method for token
