What does French degrees mean in practice?
One French degree corresponds to 10 mg CaCO3/l and is a different scale than the German degree.
When does it matter?
The same number in °fH means lower hardness than in °dH, which may significantly change the selection of the device.
Which solutions are related to it?
The unit is confirmed on the report and converted to a common basis of mg CaCO3/l before comparing the results.