1. The logical record length is 400 coded characters
   containing header information, blank spaces, and data
   for one element for one hour.

2. Blocks are padded with nines (9s) internally to fill
   missing data segments and to complete a data set.

3. Each logical record contains header information and
   data in the following format: North polar distance,
   longitude, year, month, day, hour, element, observatory
   code, blank spaces, 60 data values, and an hourly mean.

   NPD     LONG   YR      MO      DA      E    HR
   1-6     7-12   13-14   15-16   17-18   19   20-21

   OBS     ORG  (Blanks)  DATA-1  DATA-60   HRly MEAN
   22-24   25     26-34   35-40   389-394   395-400

4. NPD is the observatory's North Polar Distance (0 to 180
   degrees) from the north geographic pole in thousandths
   of a degree and is alloted 6 characters. Decimal point
   is implied between positions 3 and 4.

   LONG is the geographic longitude (0 to 360 degrees)
   measured EAST from Greenwich in thousandths of a degree
   and also has a 6-character field. Decimal point is
   implied between posilions 9 and 10.

   YR, MO, DA, and HR are each 2-digit numbers giving the
   date and time in GMT. E is the element symbol in 1
   character: it may be D, H, X, Y, Z, or F.

   OBS is the 3-letter code (abbreviation) assigned by IAGA
   for the observatory.

   ORG is the origin of the data,
   e.g. G = US Geological Survey.

   Blanks are spaces for 9 characters reserved
   for future additions.

   DATA-1 ... DATA-60 are 1-minute values of the given
   element for that hour. H, X, Y, Z, or F are given to
   the nearest nanoTesla (gamma). D is given to the
   nearest tenth-minute of arc (612 = l degree + 01.2
   minutes East). Each value is in a 6-character field.

   HRly MEAN is the average of the preceding 60
   1-minute values.

5. Each element value and the hourly mean is given in
   a six-digit field including a minus sign for negative
   values, or a blank for positive values.

6. Missing data spaces are padded with 99999. No
   alteration of logical record length is required
   for different types of computers.

7. Positive values of Declination (D) indicate East
   Declination and negative values indicate
   West Declination.

   Codes for sources of digital magnetometer data in
   the WDC system not only indicate the source
   organization, but also show whether the data are
   average values or point data. For example, 1-minute
   point values scaled from analog magnetograms for
   the production of AE indices are coded with a "D"
   because they are "digitized".
   Typically, digital 1-minute values received by WDCs
   from organizations operating automatic magnetic
   observatory instruments are averages of more
   frequendy sampled values, e.g. 10-second point samples.
   Different organizations process their higher time
   resolution observations in different ways. Some may
   filter and smooth the observations. Some follow the
   practice recommended by IAGA of averaging higher time
   resolution samples from before and after the minute
   to obtain a 1-minute value centered exactly on the
   minute. Others average values from the beginning of a
   given minute to the beginning of the next minute,
   effectively centering the mean on the half-minute,
   in similar fashion to the processing of 1-minute values
   to obtain hourly means. If the method used to obtain
   1-minute average values is important to a user, the WDC
   will assist in determining the exact procedure applied.

   In general, digital values from national networks are
   "absolute" and are tied to baselines determined by are
   operating institutions. Often only timely variations
   data are needed to support special research campaigns
   and digital values may be transmitted from regular
   observatory sites via satellite relay platforms. Such
   values are "flagged" with a "V" as noted below and
   eventually are replaced by the standard digital
   observatory output. Values from special networks such
   as the IMS chains are variations only.  Attempts are
   made to check the absolute output of these instruments
   but usually no systematic absolute observations are
   possible or they are later replaced by adopted
   standard observatory digital values.

  ORG (data origin codes)

   A = Alaskan meridian magnetometer chain
       (includes Canadian sites) for IMS
   C = Canadian standard observatory network
   O = point samples digitized from analog magnetograms
   F = France
   G = USGS standard observatory network
       (one station operated by NOAA)
   J = Japan
   K = US AFGL E-W sub-auroral zone magnetometer chain
   R = Western Canadian meridian magnetometer chain
       operated for IMS
   T = Lungping magnetic observatory, Taiwan.
   U = E-W mid-latitude magnetometer chain operated for IMS
   V = Variations only sent via NOAA GOES satellite relay
   W = Eastern Canadian meridian magnetometer chain
       operated for IMS