Hi Pierce
I think your confusion stems from the fact that the various totals don't all work in the same way.
"1 hour" and "24 hours" measure back from "now", either 1 hour or 1 day, and so potentially change minute by minute.
"Weekly", on the other hand, is NOT the week working back from "now". Instead, a specific week starting at midnight is used. This is determined by when you first start the station (or factory reset it). So if you powered it up today (Monday), the "weekly" count would start at midnight tomorrow night, and so the station would always show a Wednesday to Tuesday (inclusive) week.
"Monthly" similarly works on a fixed period, this time, the CALENDAR month. So "last month" would currently be showing the total rainfall recorded for January 2014. Later this week when we move into March, this will switch to the total for February 2014. So for a given month, the amount you see will never change. Clearly, unless you happen to start up on the first of a month, the first month's figure will be a partial one.
"Total" is different again. It shows all accumulated rainfall since its last manual reset, so will just keep rising until you reset it.
Good luck!
Fred