## Create a list of PCICt of length 2 with a 365-day calendar
x <- as.PCICt(c("1961-09-02", "1963-02-01"), cal="365_day")
## Look at the difference between the two elements of x
y <- x[1] - x[2]
## Change the first element of x
x[1] <- as.PCICt("1962-09-02", cal="365_day")
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