As stated earlier, the most common size of mobile computing device is pocket-sized that can be hand-held, but other sizes for mobile devices exist, too. Mark Weiser, known[by whom?] as the father of ubiquitous computing, computing everywhere, referred to device sizes that are tab-sized, pad and board sized, where tabs are defined as accompanied or wearable centimetre-sized devices, e. g. smartphones and smart cards, and pads are defined as hand-held decimetre-sized devices, e. g. , laptops and tablets. If one changes the form of the mobile devices in terms of being non-planar, one can also have skin devices and tiny dust-sized devices. Dust refers to miniaturised devices without direct HCI interfaces, e. g. , micro electro-mechanical systems (MEMS), ranging from nanometres through micrometers to millimetres. See also Smart dust. Skin: fabrics based upon light emitting and conductive polymers and organic computer devices. These can be formed into more flexible non-planar display surfaces and products such as clothes and curtains, see OLED display. Also see smart device.