Accumulation

[OLLCommander]

When I click on a time on a forecast and it shows the accumulation in brackets as 3 hours, is that 3 hours up to the time, the 3 hours after the time, or 1 hour either side?

For example, if I click rain, slide to 15:00, click the weather picker on the map and it says 4mm, is that the accumulated rain from 12:01 to 15:00, 15:00 to 17:59, or 14:00 to 16:59?

Also, I notice that the weather forecast bar and weather picker show different amounts of rain for the same time and location, why?