CHAPTER 2
METEROLOGICAL TABLES AND CHARTS
SECTION IGENERAL TABLES AND CHARTS FOR METEOROLOGICAL MESSAGES 
21. Description of Tables and Charts
The tables and charts in this manual are presented in sections I, II, and III as follows:
a. Section I, General Tables and Charts for Meteorological Messages. These tables and charts are used for computing general meteorological data from all types of meteorological messages.
b. Section II, Tables for Type 2 (Electronic), Ballistic Message for SurfacetoAir Trajectories. These tables include the weighting factors and the weighted quantities for density, wind, and temperature pertaining to the trajectories of air defense weapons (guns).
c. Section III, Departure Tables for Type 2 (Visual), Ballistic Message for SurfacetoAir Trajectories. These departure tables are used in determining ballistic densities for a type 2 message.
22. Zone Structure of Atmosphere
For convenience in computing, reporting, and applying corrections, the standard atmosphere is further identified by dividing it into zones for standard heights. The zones for the various meteorological messages are illustrated in figure 21.
23. Horizontal Distance Tables
a. Horizontal distance tables (table 21) are computed for the standard heights of the zone structure as shown in figure 2l and for a curved earth surface according to the following formula:
b. In this formula, D is the arc distance of the earth's surface in meters and q is the elevation angle to a balloon at standard height H. R is the average radius of the earth, 6,367,650 meters.
24. Conversion of Wind Speed (Miles per Hour to Knots)
Chart 21 is used to convert wind speed in knots and miles per hour.
25. Pressure Conversion (Inches of Mercury to Millibars)
The millibars of pressure for a certain number of inches of mercury may be determined from chart 22.
26. Conversion of Pressure to Percent of Standard
The conversion of surface pressure in millibars to percent of the standard mean sea level (MSL) pressure is accomplished by use of chart 23.
27. Pressure to Contact Conversion
The conversion of pressure in millibars to contact value in tenths, or vice versa, is accomplished by use of table 24.
Relative humidity may be determined by use of a psychrometer and psychrometer tables or by use of chart 24.
29. Table of Corrections Used to Determine Virtual Temperature for Plotting Chart ML574( )
a. Table 25 provides temperature multipliers which, when multiplied by relative humidity values (i.e., 45% = 0.45, etc.) and added to the observed temperature values, yield virtual temperatures.
b. Enter the table with the observed air temperature rounded off to the nearest whole degree Celsius and the observed pressure rounded off to the nearest 50 millibars. If the observed pressure value ends with 25 or 75 (e.g., 925 or 775), round off to the lower 50millibar value. Do not interpolate.
210. Conversion of Surface Density to Percent of Standard
The surface density, in grams per cubic meter and expressed as a standard surface density, may be determined from chart 25.
SECTION IITABLES FOR TYPE 2, BALLISTIC MESSAGE FOR SURFACETOAIR TRAJECTORIES 
Tables 28 through 214 contain the weighting factors used in obtaining a type 2 message. Some of the tables present the weighting factors directly; in others, the weighting factors are used to determine the effect of the various zone values on the line values of the meteorological message. The weighting factors used are those agreed to, on an interim basis, by the fifth meeting of the NATO Group on External Ballistics, November 1960.
212. Weighted Density Tables (Type 2 Message)
a. The weighted density tables give the weighted densities for the type 2 message (surfacetoair firing) and may be used to convert zone densities in grams per cubic meter to zone densities in percent of standard for that zone, and to convert zone densities to the weighted effect of these zone densities on the various line values of the meteorological message.
b. The values in the densitypercent column were computed by dividing the Gm/M^{3} value by the zone midpoint standard density.
c. The linezone number values were computed by multiplying the density percent values by the weighting factors shown in table 28. Linezone number 21 is the product of the weighting factor (.63), line 2 of zone number 1, table 28 and the densitypercent value. Linezone number 32 is the product of the weighting factor (.37), line 3 of zone number 2, table 28 and the densitypercent value.
213. Weighted Wind Speed Tables (Type 2 Message)
a. The weighted wind tables maybe used to convert zone winds to the weighted effect of these winds on various line values of the meteorological message.
b. The linezone number values are the product of zone wind values and the weighting factor values shown in table 210. The values of linezone number 21 are the product of zone wind speeds and the weighting factor (.50), line 2 of zone number 1, table 210.
214. Weighted Temperature Tables (Type 2 Message)
a. The weighted temperature tables may be used to convert zone temperatures in degrees Celsius to zone temperatures in percent of standard for each zone. They may also be used to convert zone temperatures to the weighted effect of temperatures on the various line values of the meteorological message.
b. The zone temperaturepercent column is the quotient of the zone temperature divided by the standard zone temperature.
c. The linezone number values are the product of the weighting factors shown in table 212 and the zone temperaturepercent values. The linezone number values of column 21 are the product of the weighting factor (.63), line 2 of zone number 1, table 212, and the zone temperaturepercent values.
SECTION IIIDEPARTURE TABLES FOR TYPE 2 (VISUAL) BALLISTIC MESSAGE FOR SURFACETOAIR TRAJECTORIES 
The tables and charts contained in this section are used to determine the departure from mean surface density for the computation of a ballistic meteorological message (visual).
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