Siemens sinumerik 840D sl Operating Manual page 488

Multi-channel support
9.4 Simulating a machining operation
Note
The 2 window view cannot be activated if you have simultaneously selected the main spindle
and the counterspindle.
488
Press the "3D view" softkey if you wish to view the workpiece as
a three-dimensional model.
- OR -
Press the 2-window softkey if you wish to simultaneously view
the side view (left-hand window) and front view (right-hand
window) of the workpiece.
Operating Manual, 07/2010, 6FC5398-8CP40-0BA0
Turning