Most operating systems support multiple monitors.
When a touchscreen is used in a multi-monitor setup the configuration can be quite straight-forward and at other times more complex.
When using two or more monitors on a system they could be laid out in a row (horizontal) or stacked (vertical) or any combination thereof.
The desktop could be extended across all monitors or the desktop could be mirrored on each monitor.
The operating system's view of the monitors could match the physical number of monitors connected or it could see only one or more logical monitors although there are many more physical monitors.
We have put a lot of effort into being able to support all the various multi-monitor configurations such that the relationship between the physical touch screen and the underlying video metrics is correct.
The bottom line is that when the driver receives a touch that is to be posted on one of the operating systems interfaces the positional request must be such that the point of touch is at the correct position on the desktop.
Where the multi-monitor setup is quite straight-forward (OS view of the monitors is the same as the physical number) the UPDD Configuration tool will likely create the correct desktop / touch association.
For any other layouts it may be necessary to manually define the monitor configuration and segmentation prior to using the configuration tool as described in our multi-monitor documentation.
Particularly in Linux multiple monitor definitions can be very complex, hence we have written a Linux specific multi-monitor document.