This article address using the active stylue pen while touching the touchscreen with your finger at the same time.

When using the Active Stylus Pen on the 03-Series IDS monitors (currently 3203L, 4303L, 5053L, 5503L, 5553L and 6553L) you cannot use a finger at the same time. See below information from page 26 of the product User's Guide.

Stylus (Active)
Elo provides active stylus pens that can be used on the projected capacitance version of the 03-Series IDS monitor.
Elo Active Stylus Part Number: E216215
Note: The minimum distance between two monitors should be 72cm (28.35in) ±10%

Features of the stylus include Auto power off, pressure detection, right click, erase and pen priority.

• To use pressure sensing, apply pressure to the screen and the object that is being drawn will become thicker. Release pressure to make the object thinner.
• To use the right click feature, press the button closest to the tip of the stylus.
• To use the erase feature, press the button away from the tip of the stylus.
• Side buttons follow Microsoft HID digitizer specification and functionality depends on applications definition.
• Pen priority – Touch priority is given to the stylus. If a stylus and finger are present, then the touch will follow the stylus.
• A custom API must be created in order to use two stylus pens at the same time.