This is an instance in which the original patent document by which we found the classification does not display the nature of the classification. This classification may involve peculiarities of design and technical principle which are not at all exclusive to aeronautics. That this has to do with instruments is highly likely. That it includes all instruments is extremely unlikely. That the broader AT 42 includes most instruments is rather speculative.
This wiki has 1 patents in category "AT 42i".
Patents in category AT 42i
- Patent AT-1911-51955 (English title: Apparatus for detecting upper fog or cloud boundaries using captive balloons or kites, Filing date: 1910-12-07)
|Enclosing categories||Austrian patent classifications, AT 42, Patent classification systems|