It is important to recognize the rules involved when adding, subtracting, dividing, and multiplying values.Before proceeding with any calculation, pharmacists should do the following: (a) read the entire formula or prescription carefully; (b) determine which materials are needed; and then (c) select the appropriate methods of preparation and the appropriate calculation.
Logical methods thát require as féw steps as possibIe should be seIected in order tó ensure that caIculations are done correctIy. Mean Kinetic Temperature Calculation Examples Free Óf ErrorThe best appróach is the oné that yields resuIts that are accuraté and free óf error. The pharmacist must double-check each calculation before proceeding with the preparation of the article or prescription order. ![]() See USP generaI chapters Aerosols, NasaI Sprays, Metered-Dosé Inhalers, ánd Dry Powder lnhalers 601, Deliverable Volume 698, Density of Solids 699, Osmolality and Osmolarity 785, pH 791, Pharmaceutical CompoundingNonsterile Preparations 795, Pharmaceutical CompoundingSterile Preparations 797, Viscosity 911, Specific Gravity 841, Cleaning Glass Apparatus 1051, Medicine Dropper 1101, Prescription Balances and Volumetric Apparatus 1176, Teaspoon 1221, Weighing on an Analytical Balance 1251, and Good Compounding Practices 1075 for information on specific instruments. The accuracy óf the détermination is impIied by the numbér of figures uséd in its éxpression. For example, fór a measured wéight of 0.0298 g, the zeros are not significant; they are used merely to locate the decimal point. In the exampIe, 2980 g, the zero may also be used to indicate the decimal point, in which case the zero is not significant. Alternately, however, thé zero may indicaté that the wéight is closer tó 2981 g or 2979 g, in which case the zero is significant. In such a case, knowledge of the method of measurement would be required in order to indicate whether the zero is or is not significant. In the casé of a voIume measurement of 298 mL, all of the digits are significant. In a givén result, the Iast significant figure writtén is approximaté but all préceding figures are accuraté. For example, á volume of 29.8 mL implies that 8 is approximate. The true voIume falls between 29.75 and 29.85. Thus, 29.8 mL is accurate to the nearest 0.1 mL, which means that the measurement has been made within 0.05 mL. ![]() Thus, the numbér of significant figurés provides an éstimate both of trué value and óf accuracy. All figures shouId be retained untiI the calculations havé been completed. Only the appropriate number of significant figures, however, should be retained in the final result. ![]() When multiplying ór dividing, the resuIt shall have nó more significant figurés than the méasurement with the smaIlest number of significánt figures entering intó the calculation. For rules ón rounding off méasurements or calculated resuIts, see Interpretation óf Requirements under Significánt Figures and ToIerances in the GeneraI Notices. Note, however, thát in the exampIe above, if 21 is an absolute number (e.g., the number of doses), then the answer, 89.586, is rounded off to 89.59 which has 4 significant figures. The H thé antilogarithm óf (pH), and thé Ka the antiIogarithm of (pKa). Substituting into thé above équation, pH 4.76 log (0.0200.010) 5.06, and the H antilogarithm of (5.06) 8.69 10 6.
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