At a great rate of knots.
Ingo there is a very good reason to use metric. We used to use imperial inches but metric makes more sense. If you take 1 litre of water in pour it into a dish that is 1 meter square the water will be 1mm deep. So when someone says we have had 25mm of rainfall then it is much easier to envisage how much water has actually fallen. Even though I grew up with the inches measurement I'm still not sure exactly what it means.