Hi Dennis, Thanks for your reply. I thought that the tank would have to be an indicator to receive data from within the program and display it on the front panel and that a control receives data from the front panel and returns it to the program. I now realise this is not the case but it is a bit confusing to call something that is displaying or indicating data from within the prgram a 'control'.
Once I changed the tank indicator to a control the sub vi terminal worked ok as an input. Thanks for your help. Dave G
