To compare Acqknowledge v3.9 HRV analysis results with a third-party program, you should export the interpolated tachogram data into the other program. To do this, check the Interpolated Tachogram Output option in HRV dialog box. When the HRV analysis is run, the system will display a new graph window that contains the interpolated tachogram data. The interpolated tachogram data is the last point in the analysis routine, prior to the Power Spectral Density analysis taking place and is the best data to use for comparative purposes.