I purchaced one plugable HDMI/DVI dual outplut dock and it worked great. I purchaced 7 more for my school and they are not consistently detecting the HDMI ports (the ClearTouch displays they are plugged in to are not consistently detecting that they are plugged in to a video source.
Sometimes rebooting the computer works
Sometimes rebooting the display works
Sometimes re-seating the HDMI cable works
Sometimes replacing the hdmi cable works
Sometimes one of the above worked before and now nothing works.