The composite volume output on the front of the MPVS Ultra unit should only be utilised when using a multi-segment catheter for large animal PV studies. The composite output is a combination of all the individual Volume outputs from the separate catheter segments, so when connected to the PowerLab allows you to visualise the combined Volume in one channel of LabChart.
When using single segment catheters, there is only one volume measurement. In this case you should use Output S1 on the MPVS Ultra unit and NOT the composite output.