There is stuff I've read here and there that the U3 has (0-)2.44V analog input or 3.6V. For example
//Request a read of AIN1 using the special 0-3.6 volt range. AddRequest (lngHandle, LJ_ioGET_AIN_DIFF, 1, 0, 32, 0);
But what is making it go to 3.6V range? Is it the 32 in x1? I thought that was the return for the differential? In the header it says that 32 means to add Vref. This 32 in x1 obvioiusly has special meaning but it seems to be variable. I am currently reading about 3.0V on the input so I am assuming it is working.
It is really difficult to find something in the documentation - often it is just fragments in code examples. I couldn't find a list of all the IOType values to use (apart from the definitions in the header). There doesn't seem to be cross referencing of these with the other parameters (normal channel numbers would normally appear obvious but there are issues like what to put in x1 and when).