# Gravity, Elevation And Temperature Barometer Reading Correction Calculator

This calculator requires the use of Javascript enabled and capable browsers. This script determines the error in an observed barometer reading, based on gravity differences in different latitudes, barometer elevation differences from sea level, and on temperature expansion and contraction differences. Because the Earth is not a perfect sphere, the acceleration due to gravity depends on latitude. The radius of the earth is greater at the equator than at the poles. This means that gravity is least at the equator and greatest at the poles. Thus at smaller latitudes the mercury in the barometer tube weighs less, and will require a greater length to balance a given pressure. The barometer is calibrated for a latitude of 45 degrees, at sea level. For latitudes less than 45 degrees, the correction should be subtracted from the observed height; for latitudes greater than 45 degrees the correction should be added. The metal housing of the barometer and the mercury both expand as the temperature increases. However, they expand at different rates. The barometer is calibrated for 0 degrees C, at sea level. For different temperatures a correction must be applied to compensate for the different expansions of the housing and the mercury. For temperatures greater than 0 degrees C, the correction should be added to the observed height; for temperatures less than 0 degrees C, the very minor correction should be subtracted. Contraction differences are extremely small and almost negligible. For elevation, the barometer is also calibrated at sea level; the higher the elevation, the lower the pressure. With the barometer at elevations above sea level, the correction should be added since it is a negative value; below sea level, the value is also added but the value is positive. The default values are typical for the general lower desert area of Southern California. If you wish to show below sea level changes, just use a negative number for the appropriate elevation. To use the calculator, enter the temperature, the elevations, the latitude and the known and observed barometer reading, in any of the designations, then click on Calculate. Results are returned in both inches of mercury and millibars. If you don't know the latitude, you can use our USA longitude and latitude map to get an idea of the general area. There are also temperature, elevation and latitude correction charts below the calculator. Other pressure correction calculators are for temperature correction only, for altitude correction only, for gravity (latitude) correction only, for temperature and altitude correction.

 Unit Number Required Data Entry Latitude degrees Air Temperature Degrees C              F Elevation Of Barometer ASL Meters         Feet Observed Barometer Reading Inches Hg  Millibars Calculated Results Actual Barometer Correction inches of mercury Rounded Barometer Correction inches of mercury Actual Barometer Corrected inches of mercury Rounded Barometer Corrected inches of mercury Actual Barometer Correction millibars Rounded Barometer Correction millibars Actual Barometer Corrected millibars Rounded Barometer Corrected millibars

## Correction Chart For Relative Expansion Of Mercury And Brass Scale To 32°F Standard

 Temp hg col °F Observed reading of the barometer, in inches 25 25.5 26 26.5 27 27.5 28 28.5 29 29.5 30 30.5 31.0 Correction to be subtracted from observed reading 40 .026 .026 .027 .027 .028 .028 .029 .029 .030 .030 .031 .031 .032 42 .030 .031 .032 .032 .033 .033 .034 .035 .035 .036 .036 .037 .038 44 .035 .036 .036 .037 .038 .038 .039 .040 .040 .041 .041 .042 .043 46 .039 .040 .041 .042 .043 .043 .044 .045 .046 .046 .047 .048 .049 48 .044 .045 .046 .047 .047 .048 .049 .050 .051 .052 .053 .054 .054 50 .048 .048 .050 .051 .052 .053 .054 .055 .056 .057 .058 .059 .060 52 .053 .054 .055 .056 .057 .058 .059 .060 .061 .062 .064 .065 .066 54 .057 .059 .060 .061 .062 .063 .064 .066 .067 .068 .069 .070 .071 56 .062 .063 .064 .066 .067 .068 .069 .071 .072 .073 .074 .076 .077 58 .066 .068 .069 .070 .072 .073 .074 .076 .077 .078 .080 .081 .082 60 .071 .072 .074 .075 .077 .078 .080 .081 .082 .084 .085 .087 .088 62 .076 .077 .079 .080 .082 .083 .085 .086 .088 .089 .091 .092 .094 64 .080 .082 .083 .085 .086 .088 .090 .091 .093 .095 .096 .098 .099 66 .085 .086 .088 .090 .091 .093 .095 .096 .098 .100 .101 .103 .105 68 .089 .091 .093 .094 .096 .098 .100 .102 .103 .105 .107 .109 .110 70 .094 .095 .097 .099 .101 .103 .105 .107 .109 .110 .112 .114 .116 71 .096 .098 .100 .102 .103 .105 .107 .109 .111 .113 .115 .117 .119 72 .098 .100 .102 .104 .106 .108 .110 .112 .114 .116 .118 .120 .122 73 .100 .102 .104 .106 .108 .110 .112 .115 .116 .118 .120 .122 .124 74 .103 .105 .107 .109 .111 .113 .115 .117 .119 .121 .123 .125 .127 75 .105 .107 .109 .111 .113 .115 .117 .119 .122 .124 .126 .128 .130 76 .107 .109 .111 .113 .116 .118 .120 .122 .124 .126 .128 .131 .133 77 .109 .112 .114 .116 .118 .120 .122 .125 .127 .129 .131 .133 .136 78 .112 .114 .116 .118 .120 .123 .125 .127 .129 .132 .134 .136 .138 79 .114 .116 .118 .121 .123 .125 .127 .130 .132 .134 .137 .139 .141 80 .116 .118 .121 .123 .125 .128 .130 .132 .135 .137 .139 .142 .144 81 .118 .121 .123 .125 .128 .130 .132 .135 .137 .140 .142 .144 .147 82 .121 .123 .125 .128 .130 .133 .135 .137 .140 .142 .145 .147 .149 83 .123 .125 .128 .130 .133 .135 .138 .140 .142 .145 .147 .150 .152 84 .125 .128 .130 .133 .135 .138 .140 .143 .145 .148 .150 .153 .155 85 .127 .130 .132 .135 .137 .140 .143 .145 .148 .150 .153 .155 .158 86 .130 .132 .135 .137 .140 .142 .145 .148 .150 .153 .155 .158 .161 87 .132 .134 .137 .140 .142 .145 .148 .150 .153 .155 .158 .161 .163 88 .134 .137 .139 .142 .145 .147 .150 .153 .155 .158 .161 .163 .166 89 .136 .139 .142 .144 .147 .150 .153 .155 .158 .161 .164 .166 .169 90 .138 .141 .144 .147 .150 .152 .155 .158 .161 .163 .166 .169 .172 92 .143 .146 .149 .152 .154 .157 .160 .163 .166 .169 .172 .174 .177 94 .147 .150 .153 .156 .159 .162 .165 .168 .171 .174 .177 .180 .183 96 .152 .155 .158 .161 .164 .167 .170 .173 .176 179 .182 .185 .188 98 .156 .160 .163 .166 .169 .172 .175 .178 .181 .185 .188 .191 .194 100 .161 .164 .167 .171 .174 .177 .180 .183 .187 .190 .193 .196 .200

## Correction Of Mercurial Barometer For Latitude In Inches Hg To Reduce To 45 Degrees Latitude

or subtracted from barometer readings for latitudes below 45 degrees.

 Latitude Reading of the barometer, in inches 18 19 20 21 22 23 24 25 26 27 28 29 30 0 90 0.047 0.049 0.052 0.054 0.057 0.060 0.062 0.065 0.067 0.070 0.073 0.075 0.078 5 85 .046 .048 .051 .054 .056 .059 .061 .064 .066 .069 .071 .074 .077 6 84 .046 .048 .051 .053 .056 .058 .061 .063 .066 .068 .071 .073 .076 7 83 .045 .048 .050 .053 .055 .058 .060 .063 .065 .068 .071 .073 .075 8 82 .045 .047 .050 .052 .055 .057 .060 .062 .065 .067 .070 .072 .075 9 81 .044 .047 .049 .052 .054 .057 .059 .062 .064 .067 .069 .071 .074 10 80 .044 .046 .049 .051 .054 .056 .058 .061 .063 .066 .068 .071 .073 11 79 .043 .046 .048 .050 .053 .055 .058 .060 .062 .065 .067 .070 .072 12 78 .043 .045 .047 .050 .052 .054 .057 .059 .062 .064 .066 .069 .071 13 77 .042 .044 .047 .049 .051 .054 .056 .058 .061 .063 .065 .068 .070 14 76 .041 .043 .046 .048 .050 .053 .055 .057 .059 .062 .064 .066 .069 15 75 .040 .043 .045 .047 .049 .052 .054 .056 .058 .061 .063 .065 .067 16 74 .040 .042 .044 .046 .048 .051 .053 .055 .057 .059 .061 .064 066 17 73 .039 .041 .043 .045 .047 .049 .052 .054 .056 .058 .060 .062 .064 18 72 .038 .040 .042 .044 .046 .048 .050 .052 .054 .057 .059 .061 .063 19 71 .037 .039 .041 .043 .045 .047 .049 .051 .053 .055 .057 .059 .061 20 70 .036 .038 .040 .042 .044 .046 .048 .050 .052 .054 .056 .058 .060 21 69 .035 .037 .038 .040 .042 .044 .046 .048 .050 .052 .054 .056 .058 22 68 .034 .035 .037 .039 .041 .043 .045 .047 .048 .050 .052 .054 .056 23 67 .032 .034 .036 .038 .040 .041 .043 .045 .047 .049 .050 .052 .054 24 66 .031 .033 .035 .036 .038 .040 .042 .043 .045 .047 .049 .050 .052 25 65 .030 .032 .033 .035 .037 .038 .040 .042 .043 .045 .047 .048 .050 26 64 .029 .030 .032 .033 .035 .037 .038 .040 .041 .043 .045 .046 .048 27 63 .027 .029 .030 .032 .033 .035 .037 .038 .040 .041 .043 .044 .046 28 62 .026 .028 .029 .030 .032 .033 .035 .036 .038 .039 .041 .042 .043 29 61 .025 .026 .027 .029 .030 .032 .033 .034 .036 .037 .038 .040 .041 30 60 .023 .025 .026 .027 .028 .030 .031 .032 .034 .035 .036 .038 .039 31 59 .022 .023 .024 .026 .027 .028 .029 .030 .032 .033 .034 .035 .036 32 58 .020 .022 .023 .024 .025 .026 .027 .028 .030 .031 .032 .033 .034 33 57 .019 .020 .021 .022 .023 .024 .025 .026 .027 .028 .029 .031 .032 34 56 .017 .018 .019 .020 .021 .022 .023 .024 .025 .026 .027 .028 .029 35 55 .016 .017 .018 .019 .019 .020 .021 .022 .023 .024 .025 .026 .027 36 54 .014 .015 .016 .017 .018 .018 .019 .020 .021 .022 .022 .023 .024 37 53 .013 .014 .014 .015 .016 .016 .017 .018 .019 .019 .020 .021 .021 38 52 .011 .012 .013 .013 .014 .014 .015 .016 .016 .017 .018 .018 .019 39 51 .010 .010 .011 .011 .012 .012 .013 .013 .014 .015 .015 .016 .016 40 50 .008 .009 .009 .009 .010 .010 .011 .011 .012 .012 .013 .013 .013 41 49 .006 .007 .007 .008 .008 .008 .009 .009 .009 .010 .010 .010 .011 42 48 .005 .005 .005 .006 .006 .006 .006 .007 .007 .007 .008 .008 .008 43 47 .003 .003 .004 .004 .004 .004 .004 .005 .005 .005 .005 .005 .005 44 46 .002 .002 .002 .002 .002 .002 .002 .002 .002 .002 .003 .003 .003 45 45 .000 .000 .000 .000 .000 .000 .000 .000 .000 .000 .000 .000 .000

## Correction For Elevation In Inches Hg Per 100 Foot Difference In Elevation

To be added to barometer readings when above the datum plane or
subtracted from barometer readings when below the datum plane.

 Altitude ft Temperature, °F 0 10 20 30 40 50 60 70 80 90 0 .122 .119 .117 .114 .112 .110 .108 .106 .104 .102 1000 .118 .115 .113 .110 .108 .106 .104 .102 .100 .098 2000 .113 .110 .108 .106 .104 .102 .100 .098 .096 .094 3000 .108 .106 .104 .102 .100 .098 .096 .094 .092 .090 4000 .104 .102 .100 .098 .096 .094 .092 .090 .088 .086 5000 .100 .098 .096 .094 .092 .090 .088 .086 .084 .082 6000 .096 .094 .092 .090 .088 .086 .084 .082 .081 .080 7000 .093 .091 .089 .087 .085 .084 .082 .080 .079 .078

Updated 8.17.11

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