APPENDIX IGLOSSARYMany terms have different meanings when used in relation to differentsubjects. The definitions in this glossary of terms are meant to be used inconjunction with the subject matter within this text.ACCIDENTAL ERROR—Any small erroraccidentally incurred in a measurement. Unlikesystematic errors, accidental errors are notgoverned by fixed laws. They are as likely to bepositive as negative, and the theory of probabilityis based on the occurrence of these errors.ACCURACY—The degree of conformity with astandard or the degree of perfection attained ina measurement. Accuracy relates to the qualityof a result and is distinguished from precision,which relates to the quality of the operation bywhich the result is obtained.ACTUAL ERROR—The difference between theaccepted value and the measured value of aphysical quantity.ACUTE ANGLE—An angle of less than 900.ADJUSTED POSITION—An adjusted value forthe horizontal or vertical position of a surveystation, in which discrepancies due to errors inthe observed data are removed. This adjustmentforms a coordinated and correlated system ofstations.ADMIXTURE—A material other than water,aggregates, and portland cement (includingair-entraining portland cement and portlandblast-furnace slag cement) that is used as aningredient of concrete and is added to the batchimmediately before or during its mixing.ADSORBED MOISTURE—In soil mechanics,the thin films of moisture that may surround andcling to the individual particles in a soil massbecause of naturally occurring electrical attractionof water molecules to the soil particles.AGGREGATE—Any hard, inert, mineralmaterial used for mixing in graduated fragments.It includes sand, gravel, crushed stone, and slag.AGGREGATE, COARSE—Aggregate that isretained on the No. 8 sieve.AGGREGATE, FINE-Aggregate that passes theNo. 8 sieve.AGONIC LINE—The line along which themagnetic declination is zero.ALGEBRA—That branch of mathematics thatpertains to the relations and properties of numbersby means of letters, signs of operation, and othersymbols. Algebra includes solution of equations,polynomials, verbal problems, graphs, and so on.ALIDADE—The part of a surveying instrumentthat consists of a sighting device with index andreading or recording accessories. 1. The alidadeof a theodolite or engineer transit is the part ofthe instrument that includes the telescope,micrometer microscopes or verniers, andaccessories. These are mounted on what is calledthe “upper motion” of the instrument, and theyare used in observing direction or angle on thegraduated circle, which is mounted on the “lowermotion.” 2. The alidade used in topographicsurveying consists of a straightedge ruler carryinga telescope or other sighting device, and it is usedin plotting a direction on the plane-table sheet.If a telescope is used, the instrument is often calleda “telescopic alidade. ”ALTITUDE—1. The vertical angle between ahorizontal plane and the line to the observed ordefined object. In surveying, a positive altitudeAI-1
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