Boltek Lightning/2000 - Manual (Page 314)

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Trend Keywords
The @Trend keywords return the percentage change in one
of the stroke or flash rates. If the N parameter is not
specified, the keyword returns the percent change in the rate
between one minute ago and the current time. Values for N
that are less than 1 are not allowed, and will return the same
value as when no parameter is specified.
The parameter "N" may be either a positive integer, or a
positive real number.
Legal values for N are from 1 to 1440.
The percent change can range from -100 to infinity, though
for our purposes we limit the maximum percentage increase
to 1000000.
Here are some examples:
If the stroke rate one minute ago was 100 per minute, and the
stroke rate now is 80 per minute, the stroke rate has decreased
by 20% in the last minute. @TrendStrokeRate will return -
20; @TrendStrokeRate( 1 ) will also return a value of -20.
If the stroke rate 5 minutes ago was 80 per minute, and the
stroke rate now is 100, the stroke rate has increased by 25% in
the last 5 minutes. @TrendStrokeRate( 5 ) will return a
value of 25.
If the stroke rate 10 minutes ago was 8 per minute, and the
stroke rate now is 0, the stroke rate has decreased by 100% in
the last 8 minutes. @TrendStrokeRate( 8 ) will return -100.
If the stroke rate a minute ago was 0, and the stroke rate now
is 1 per minute, the stroke rate as increased by a factor of
infinity in the last minute. @TrendStrokeRate will return
1000000.