Use this command to select an alternative source for the Doppler input. This could be used to take measurements from Doppler signal previously recorded onto the audio track of a video recorder for example.
This enables the raw Doppler signal to be recorded together with the video image of the capillary under investigation. Data can be later captured and analysed. This can help the analysis for subjects where the is a lotof movement and hence a lot of signal dropout, or where a measurement isto be made over a long period, and disc storage is a concern.