What accounts for the different result?

> as.numeric(as.POSIXct("2012-01-13 08:10:00") - as.POSIXct("2012-01-13
00:00:00") , units='secs')
[1] 29400

> trunc(as.numeric(as.POSIXct("2012-01-13 08:10:00") -
as.POSIXct("2012-01-13 00:00:00") , units='secs') )
[1] 29399

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