There's no calibration.

Allow me to explain the issue: DOS apps expects (most of them) relative mouse coordinates ("mouse moved 10 units to the left, then 10 to the right"). Touch screen gives absolute coordinates ("mouse is at pixel 40 of a 480 pixels screen").

DOS programs then use the relative coordinates to draw a cursor at an absolute position, but you cannot "get" that information easily. Most DOS apps also apply their own mouse speed/acceleration algorithms over the given mouse relative coordinates, and again DOSBox knows nothing of this.

Thus, the touch screen coordinates and the drawn cursor can easily desynchronize.

The only solution is to try to disable any mouse acceleration support in the application, and play with the mouse speed settings (again, in the DOS applications) until they agree with the DOSBox sensitivity.