A short, auxiliary scale situated alongside the graduated scale of an instrument, by which fractional parts of the smallest division of the primary scale can be measured with greater accuracy by a factor of ten. If 10 graduations on a vernier equal 9 graduations on the micrometer drum of a sextant, when the zero on the vernier lies one-tenth of a graduation beyond zero on the micrometer drum, the first graduation beyond zero on the vernier coincides with a graduation on the micrometer drum. Likewise, when the zero on the vernier lies fivetenths of a graduation beyond zero on the micrometer drum, the fifth graduation beyond zero on the vernier coincides with a graduation on the micrometer drum.
Related Terms |
DRUM
A container with a capacity of 55 U.S. gallons.
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DRY PIPE
A perforated or slotted pipe or box inside the drum and connected to the steam outlet.
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DRUM WATER LEVEL LINE
The water level in the drum during the normal operating mode.
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LONGITUDINAL SEAM
A riveted or welded seam along the longitudinal axis of a boiler shell or drum.
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BEAT TO QUARTERS
Prepare for battle (beat = beat the drum to signal the need for battle preparation)
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BOILER DRUM
A cylindrical shell closed at both ends, designed to withstand internal pressure.
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LUG
As applied to boiler suspension, a steel eyepiece fitted and riveted or welded to the curvature of a boiler shell or drum and connected by a steel U-bolt or sling rod to overhead steel structure; used to support the weight of a boiler.
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MICROMETER DRUM SEXTANT
A marine sextant providing a precise reading by means of a micrometer drum attached to the index arm, and having an endless tangent screw for controlling the position of the index arm. The micrometer drum may include a vernier to enable a more precise reading. On a vernier sextant the vernier is directly on the arc.
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MUD OR LOWER DRUM
A pressure chamber of a drum or header type located at the lower extremity of a water- tube boiler convection bank which is normally provided with a blowoff valve for periodic blowing off of sediment collecting in the bottom of the drum.
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NOZZLE
A short flanged or welded neck connection on a drum or shell for the outlet or inlet of fluids; also a protecting spout for the outlet or inlet of fluids; also a projecting spout through which fluid flows.
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