The monitor checks HN once per minute and records a 0 for up or a 1 for down in the database. RRDTool then averages these values out nicely so that, for exampl

The monitor checks HN once per minute and records a 0 for up or a 1 for down in the database. RRDTool then averages these values out nicely so that, for example, when the graph is at weekday-resolution and you see a 50% filled bar spanning one day, then HN was down half of that day.