something is wrong here. take the first two bars, that’s one hour of rain (give or take some artifacts from zooming to this level), but if it rains for one hour at a rate of 20 mm per hour, you should have collected 20 mm of rain already. What is your station id?
edit: apparently the graph changed (for the worse) and doesn’t show accurate rain rates anymore. Cast your vote here Change in graphing rain rate if you prefer a better graph.