Thanks for your comments .. this appears to be a limitation of the Measurement VIs in LabVIEW. I don't see this limitation mentioned in the docs or on the website so I don't see a workaround. However, instead of using this VI, I input the signal into the counter input of the DAQ card, which works great and the way I should have done it in the first place .. just wondered about the 'built-in' measurement VIs..
Dave
