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[#565] Add clarification to the docs on Duration <> Period comparison

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1 parent 9e5894a commit 5205619c543db5d661c5340196d3fd835a89d62d @vspinu vspinu committed Jul 11, 2017
Showing with 8 additions and 6 deletions.
  1. +8 −6 R/periods.r
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@@ -74,12 +74,14 @@ check_period <- function(object){
#' [Interval-class] object with [as.interval()] or by adding
#' it to a date-time with "+".
#'
-#' Periods provide a method for measuring generalized timespans when we wish
-#' to model clock times. Periods will attain intuitive results at this task
-#' even when leap years, leap seconds, gregorian days, daylight savings
-#' changes, and other events happen during the period. See
-#' [Duration-class] for an alternative way to measure timespans that
-#' allows precise comparisons between timespans.
+#' Periods provide a method for measuring generalized timespans when we wish to
+#' model clock times. Periods will attain intuitive results at this task even
+#' when leap years, leap seconds, gregorian days, daylight savings changes, and
+#' other events happen during the period.
+#'
+#' Because Period represents imprecise amount of time it cannot be compared to
+#' precise timestamps as Durations and Intervals are. You need to explicitely
+#' conver to durations. See [Duration-class].
#'
#' The logic that guides arithmetic with periods can be unintuitive. Starting
#' with version 1.3.0, \pkg{lubridate} enforces the reversible property of arithmetic

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