Rain water is a liquid. Isn't measuring rainfall just calculating its capacity? The latest episode of "Cool Met Stuff" will explain why the unit for measuring rainfall is millimetres instead of millilitres. The video is now available on the "MyObservatory" mobile application and the Observatory's website for your viewing (programme is broadcasted in Cantonese).
Observatory's "Cool Met Stuff" channel (broadcast in Cantonese):
Broadcast schedule of various TV channels: