A nixie tube is an electronic device for displaying numerals or other information. The glass tube contains a wire-mesh anode, and multiple cathodes in the shape of Arabic numerals Applying power to one cathode surrounds it with an orange glow discharge. The tube is filled with a gas at low pressure, usually mostly neon and often a little mercury and/or argon. Although it resembles a vacuum tube in appearance, its operation does not depend on thermionic emission of electrons from a heated cathode. It is therefore called a cold-cathode tube (a form of gas-filled tube), or a variant of a neon lamp. Such tubes rarely exceed 40 °C (104 °F) even under the severest of operating conditions in a room at ambient temperature. The most common form of nixie tube has ten cathodes in the shapes of the numerals 0 to 9 (and occasionally a decimal point or two) but there are also types that show various letters, signs and symbols.