#
#\section{Time range}
#
#This table lists all the various value combinations to use as a time range:
#
#\begin{description}
#\item [0]
#  Forecast product valid for reference time + P1 (P1 > 0), or Uninitialized
#  analysis product for reference time (P1 = 0), or Image product for reference
#  time (P1 = 0).
#\item [1]
#  Initialized analysis product for reference time (P1 = 0).
#\item [2]
#  Product with a valid time ranging between reference time + P1 and reference time + P2.
3 Average between reference time+%ds to reference time+%ds.
#\item [4]
#  Accumulation (reference time + P1 to reference time + P2) product
#  considered valid at reference time + P2.
#\item [5]
#  Difference (reference time + P2 minus reference time + P1) product
#  considered valid at reference time + P2.
#\item [6-9] Reserved.
#\item [10]
#  P2 = 0; product valid at reference time + P1.
#\item [11-50] Reserved.
#\item [51]
#  Climatological Mean Value: multiple year averages of quantities which are
#  themselves means over some period of time (P2) less than a year. The
#  reference time (R) indicates the date and time of the start of a period of
#  time, given by R to R + P2 , over which a mean is formed; N indicates the
#  number of such period-means that are averaged together to form the
#  climatological value, assuming that the N period-mean fields are separated by
#  one year. The reference time indicates the start of the N-year climatology. N
#  is given in octets 22 and 23 of the PDS.
#
#  If P1 = 0, then the data averaged in the basic interval P2 are assumed to be
#  continuous (i.e., all available data are simply averaged together).
#
#  If P1 = 1 (the units of time - octet 18,Code table 4 - are not relevant
#  here), then the data averaged together in the basic interval P2 are valid
#  only at the time (hour, minute) given in the reference time, for all the days
#  included in the P2 period. The units of P2  are given by the contents of
#  octet 18 and Code table 4.
#\item [52-112] Reserved.
#\item [113]
#  Average of N forecasts (or initialized analyses); each product has forecast
#  period of P1 (P1 = 0 for initialized analyses); products have reference
#  times at intervals of P2, beginning at the given reference time.
#\item [114]
#  Accumulation of N forecasts (or initialized analyses); each product has
#  forecast period of P1 (P1 = 0 for initialized analyses); products have
#  reference times at intervals of P2, beginning at the given reference time.
#\item [115]
#  Average of N forecasts, all with the same reference time; the first has a
#  forecast period of P1, the remaining forecasts follow at intervals of P2.
#\item [116]
#  Accumulation of N forecasts, all with the same reference time; the first has
#  a forecast period of P1, the remaining forecasts follow at intervals of P2.
#\item [117]
#  Average of N forecasts; the first has a forecast period of P1, the
#  subsequent ones have forecast periods reduced from the previous one by an
#  interval of P2; the reference time for the first is given in octets 13 to 17,
#  the subsequent ones have reference times increased from the previous one by
#  an interval of P2. Thus all the forecasts have the same valid time, given by
#  the reference time + P1.
#\item [118]
#  Temporal variance, or covariance, of N initialized analyses; each product has
#  forecast period of P1  = 0; products have reference times at intervals of P2,
#  beginning at the given reference time.
#\item [119]
#  Standard deviation of N forecasts, all with the same reference time with
#  respect to the time average of forecasts; the first forecast has a forecast
#  period of P1, the remaining forecasts follow at intervals of P2.
#\item [120-122] Reserved.
#\item [123]
#  Average of N uninitialized analyses, starting at the reference time, at
#  intervals of P2.
#\item [124]
#  Accumulation of N uninitialized analyses, starting at the reference time, at
#  intervals of P2.
#\item [125-254] Reserved.
#\item [256]
#  When P1=0 and P2=0: General cloud group \\
#  When P1=0 and P2=1: CL \\
#  When P1=0 and P2=2: CM \\
#  When P1=0 and P2=3: CH \\
#  When P1=1 and P2=0: Vertical significance 1 \\
#  When P1=2 and P2=0: Vertical significance 2 \\
#  When P1=3 and P2=0: Vertical significance 3 \\
#  When P1=4 and P2=0: Vertical significance 4 \\
#  When P1=0 and P2=0: Extra station information
#\end{description}
#
#Notes about the time range values:
#
#\begin{itemize}
#\item For analysis products, or the first of a series of analysis products, the reference time (octets 13 to 17) indicates the valid time.
#\item For forecast products, or the first of a series of forecast products, the reference time indicates the valid time of the analysis upon which the (first) forecast is based.
#\item Initialized analysis products are allocated code figures distinct from those allocated to uninitialized analysis products.
#\item Code figure 10 allows the period of a forecast to be extended over two octets; this is to assist with extended range forecasts.
#\item Where products or a series of products are averaged or accumulated, the number involved is to be represented in octets 22 and 23 of Section 1, while any number missing is to be represented in octet 24.
#\item Forecasts of the accumulation or difference of some quantity (e.g. quantitative precipitation forecasts), indicated by values of 4 or 5 in octet 21, have a product valid time given by the reference time + P2; the period of accumulation, or difference, can be calculated as $P2 - P1$.
#\item A few examples may help to clarify the use of Code table 5:
#  \begin{itemize}
#  \item For analysis products, P1 will be zero and the time range indicator
#	(octet 21) will also be zero; for initialized products (sometimes
#	called "zero hour forecasts"), P1 will be zero, but octet 21 will be
#	set to 1.
#  \item For forecasts, typically, P1  will contain the number of hours of the
#	forecast (the unit indicator given in octet 18 would be 1) and octet 21
#	would contain a zero.
#  \end{itemize}
#\item Code value 115 would be used, typically, for multiple day mean forecasts,
#      all derived from the same initial conditions.
#\item Code value 117 would be used, typically, for Monte Carlo type
#      calculations; many forecasts valid at the same time from different
#      initial (reference) times.
#\item Averages, accumulations, and differences get a somewhat specialized
#      treatment. If octet 21 has a value between 2 and 5 (inclusive), then the
#      reference time + P1  is the initial date/time and the reference time + P2
#      is the final date/time of the period over which averaging or accumulation
#      takes place. If, however, octet 21 has a value of 113, 114, 115, 116,
#      117, 123, or 124, the P2 specifies the time interval between each of the
#      fields (or the forecast initial times) that have been averaged or
#      accumulated. These latter values of octet 21 require the quantities
#      averaged to be equally separated in time; the former values, 3 and 4 in
#      particular, allow for irregular or unspecified intervals of time between
#      the fields that are averaged or accumulated.
#\end{itemize}
#
