Millivoltmeter.  An electrical instrument that measures  voltage in units of millivolts (thousandths of a volt). Mist coat.  A very light coat of zinc chromate primer. It is  so thin that the metal is still visible, but the primer makes  pencil marks easy to see. Moisture separator.  A component in a high-pressure  pneumatic system that removes most of the water vapor  from the compressed air. When the compressed air is used,  its pressure drops, and this pressure drop causes a drop in  temperature. If any moisture were allowed to remain in the  air, it would freeze and block the system. Mold line.  A line used in the development of a flat pattern for  a formed piece of sheet metal. The mold line is an extension  of the flat side of a part beyond the radius. The mold line  dimension of a part is the dimension made to the intersection  of mold lines and is the dimension the part would have if its  corners had no radius. Mold point.  The intersection of two mold lines of a part.  Mold line dimensions are made between mold points. Moment.  A force that causes or tries to cause an object to  rotate. The value of a moment is the product of the weight of  an object (or the force), multiplied by the distance between  the center of gravity of the object (or the point of application  of the force) and the fulcrum about which the object rotates. Monel.  An alloy of nickel, copper, and aluminum or silicon. Monocoque.  A single-shell type of aircraft structure in  which all of the flight loads are carried in the outside skin  of the structure. MSDS.  Material Safety Data Sheets. MSDS are required  by the Federal Government to be available in workplaces to  inform workers of the dangers that may exist from contact  with certain materials. MSL.  Mean sea level. When the letters MSL are used with  an altitude, it means that the altitude is measured from mean,  or average, sea level. MTBF.  Mean time between failures. Multimeter.  An electrical test instrument that consists  of a single current-measuring meter and all of the needed  components to allow the meter to be used to measure voltage,  resistance, and current. Multimeters are available with either  analog-or digital-type displays. Multiple-disk brakes.  Aircraft brakes in which one set of  disks is keyed to the axle and remains stationary. Between  each stationary disk there is a rotating disk that is keyed to  the inside of the wheel. When the brakes are applied, the  stationary disks are forced together, clamping the rotating  disks between them. The friction between the disks slows  the aircraft. Nailing strip.  A method of applying pressure to the glue in a  scarf joint repair in a plywood skin. A strip of thin plywood is  nailed over the glued scarf joint with the nails extending into  a supporting structure beneath the skin. The strip is installed  over vinyl sheeting to prevent it sticking to the skin. When  the glue is thoroughly dry, the nailing strip is broken away  and the nails removed. Nap of the fabric.  The ends of the fibers in a fabric. The first  coat of dope on cotton or linen fabric raises the nap, and the  fiber ends stick up. These ends must be carefully removed  by sanding to get a smooth finish. Naphtha.  A volatile and flammable hydrocarbon liquid used  chiefly as a solvent or as a cleaning fluid. NDB.  Non-directional beacons. Negative pressure relief valve (pressurization component). A valve that opens anytime the outside air pressure is greater  than the cabin pressure. It prevents the cabin altitude from  ever becoming greater than the aircraft flight altitude. Neutral axis (neutral plane).  A line through a piece of  material that is bent. The material in the outside of the bend  is stretched and that on the inside of the bend is shrunk. The  material along the neutral plane is neither shrunk nor stretched. Neutral flame.  An oxyacetylene flame produced when the  ratio of oxygen and acetylene is chemically correct and  there is no excess of oxygen or carbon. A neutral flame has  a rounded inner cone and no feather around it. Noise (electrical).  An unwanted electrical signal within a  piece of electronic equipment. Nomex.  A patented nylon material used to make the  honeycomb core for certain types of sandwich materials.  Nonenergizing brake.  A brake that does not use the  momentum of the aircraft to increase the friction. Nonvolatile memory.  Memory in a computer that is not lost  when power to the computer is lost. G-23