Ah - there's the little bit of information I needed to find it: Serie C.

Introduced 1891 as f:6.3, changed to f:5 in 1920. That's presumably also when it became "Extra Rapid", as my references (pre-1920) don't mention the "Extra".

The first version was rated at 70 coverage, that can be assumed to have changed with the increase in speed and changes in the definition of "coverage".