The screen declares the following properties through udev:

DEVLINKS]=>value[/dev/input/by-id/usb-Chalkboard_Electronics_HID_Touchscreen-event-mouse /dev/input/by-path/platform-bcm2708_usb-usb-0:1.2:1.0-event-mouse]
[DEVNAME]=>value[/dev/input/event0]
[DEVPATH]=>value[/devices/platform/bcm2708_usb/usb1/1-1/1-1.2/1-1.2:1.0/input/input0/event0]
[ID_BUS]=>value[usb]
[ID_INPUT]=>value[1]
[ID_INPUT_TABLET]=>value[1]
[ID_MODEL]=>value[HID_Touchscreen]
[ID_MODEL_ENC]=>value[HID\x20Touchscreen]
[ID_MODEL_ID]=>value[f723]
[ID_PATH]=>value[platform-bcm2708_usb-usb-0:1.2:1.0]
[ID_PATH_TAG]=>value[platform-bcm2708_usb-usb-0_1_2_1_0]
[ID_REVISION]=>value[0001]
[ID_SERIAL]=>value[Chalkboard_Electronics_HID_Touchscreen]
[ID_TYPE]=>value[hid]
[ID_USB_DRIVER]=>value[usbhid]
[ID_USB_INTERFACES]=>value[:030000:]
[ID_USB_INTERFACE_NUM]=>value[00]
[ID_VENDOR]=>value[Chalkboard_Electronics]
[ID_VENDOR_ENC]=>value[Chalkboard\x20Electronics]
[ID_VENDOR_ID]=>value[04d8]
[MAJOR]=>value[13]
[MINOR]=>value[64]
[SUBSYSTEM]=>value[input]
[UDEV_LOG]=>value[3]
[USEC_INITIALIZED]=>value[7587083]

The following is a typical event sequence:

0006.415234: /dev/input/event0: EV_MSC MSC_SCAN 852034
0006.415234: /dev/input/event0: EV_KEY 0x014a 1
0006.415234: /dev/input/event0: EV_KEY 0x0140 1
0006.415234: /dev/input/event0: EV_ABS ABS_X 625
0006.415234: /dev/input/event0: EV_ABS ABS_Y 516
0006.415234: /dev/input/event0: EV_SYN SYN_REPORT 0
0006.491225: /dev/input/event0: EV_MSC MSC_SCAN 852034
0006.491225: /dev/input/event0: EV_KEY 0x014a 0
0006.491225: /dev/input/event0: EV_KEY 0x0140 0
0006.491225: /dev/input/event0: EV_SYN SYN_REPORT 0

The screen declares itself as ID_INPUT_TABLET, not ID_INPUT_TOUCH, so we don't recognise it.