Dashboard instrumellts to Decantation.

Dashboard instruments. (Auto. Mech.) Ammeter, speedometer, oil gauge, gasoline gauge, thermo­meter, and sometimes other instru­ments mounted on the instrument panel of an automobile.
Dashpot. (Mach.) A small cylinder which, with its piston, absorbs a part of the shock in the quick clos­ing of steam and exhaust valves l'f a Corliss engine.
Data. Points of reference, (Engin.) Generally refers to tabulated statistical information concerning a piece of work.
Datum. A point of reference.
Datum line. Any base or fundamental line from which dimensions are taken or graphic calculations made.
Daubing. (Fdry.) Filling cracks in cores, or plastering a cupola after heat. (Plaster.) Smearing or coating with plaster in an unworkmanlike . manner.
Davey. (Bookbndg.) The name of the manufacturer of the best board for book covers, which is sold under the name "Davey Board."
Davy safety lamp. A miner's safety lamp, in which the air passages are covered with a fine copper-wire screen, by means of which the products of combustion are cooled to such an extent that gases will not be ignited by them.
dBf. Decible femto watt (10-1' watts.). dB SPL. SPL is Sound Pressure Level
(i.e" an acoustical measurement). One dB SPL is the smallest audible difference in sound level. 0 dB SPL is 0.0002 dynes/square centilllclre or 20 micro-Pascals. It is also the threshold of human hearing at I kHz (the threshold of pain is between 120 and 130 dB SPL).
dBm. dBm is an electrical measure­ment of power. 0 dBm is equal to I milliwatt, which is the same as 0.775 volts across a 600 ohm impedance. (+30dBmis I watt,+50dBmis 100 watts.)
dBV. dBV is an electrical measure­ment of voltage. O.dBV is euqal to I volt. (+ io dBV is 20 volts.) dBV is also an electrical measurement of voltage, butOdBV is equal to 0.775 volts.
dBW. is an electrical measu(ement of power. 0 dBW is equal to I watt. (+ 10 dBW is 10 watts, + 20 dBW is 100 watts.)
dbx. Compander-type commercial noise reduction system whch re­sponds to overall dynamics of sig­nals without a.particular reference level.
DC. Direct current. In batteries for use on portables this is commonly 12 volts.
D.C Bias. A method of establishing the operating point for recording
by means of an unidirectional mag­netic field. This method is charac­terised by high noise and distortion compared to a.c. Bias Recording and is used only in the most com­pact of inexpensive equipment.
D.C. Erasure. Erasure by means of an unidirectional magnetic field which leaves the tape in a saturated state. This method of erasure in­

D.C. Noise. The noise observed. on playback of a tape which has been subjected to a unidirectional mag­netic field such as in a cheap 'bulk eraser' .
Dead. (P.rint.) A type form is "dead" when it has been printed and is ready for distribution.
Deadbeat. (Elec.) Instruments ~here indicators come promptly to a po­sition of rest due to heavy damping.
DeJld center. (Mach. and Wood Turn.) The center which is fitted into the tail stock of a lathe and does not rotate with the work.
Dead end. (Plumb.) The extended portion of a pipe which is closed at.one end, and to which no connec­tions are made on the extended portion, thus permitting the stagna­tion of water or air therein.
Deadening. (Arch.) The soundproof­ing of floors and walls by the use of insulating materials made for that purpose.
Dead level. An emphatic expression in the sense of absolute lev.eL
Dead line. (Print.) (I) A line marked on the bed of a cylinder press as a guide for placing the form. (2) The last hour or day when copy will be accepted. .
Dead load. (Engin.) A load whose . pressure is steady and constant.
Dead matter. (Print.) Type matter not to be used, or type ready .to be dis­tributed.
Dead rear axle. (Auto.) A fixed rear axle that cannot turn. Use<t on double-chain-driven cars and in­ternal-gear-drive trucks.
Dead rise. (Aero.) In a cross-section of a float or flying-boat hull, the amount by which the height of the chine differs from that of the keel.
Dead-smooth file. (Mech.) The fin­est cut file made.
Dead spot. (Radio.) Some locality at which is natural phenomenon pre­vents the reception of radio waves at certain frequencies.
Dead weight. (Engin.) The .weight 0." a vehicle or carrier itself as dis­tingUished from carried or live load.
Deal. (Carp.) A board or plank, or the wood of which the board or plank is made.
Decade resistance box. (Elec.) A simple form of resistance box con­taining two sets of ten coils, one set of one ohm resistance each, and the other of ten ohms' resistance each. Also called a "decimal rheo­stat."

De calage. (Aero.) The acute angle between the wing chords of a bi­plane or multiplane.
Decalcomania. (Paint.) A process of transferring prints or pictures from paper to some smooth surface, such as glass, porcelain, wood, etc. Such a print before transferring.
Decalin. (Chern.) A turpentine sub­stitute - C1oH16. Also used as a solvent for fats, resins, and oils. Chemically, it is known as decahydronaphthalene. .
Decantation. (Chern.) Pouring off the clear liquid from the top of a sus­
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