Drop protocol to obtain an analog computer (5,4)
I believe the answer is:
slide rule
'an analog computer' is the definition.
(slide rule is a kind of analog computer)
'drop protocol' is the wordplay.
'drop' becomes 'slide' (I've seen this before).
'protocol' becomes 'rule' (I can't explain this - if you can you should believe this answer much more).
'slide'+'rule'='SLIDE-RULE'
'to obtain' is the link.
Can you help me to learn more?
(Other definitions for slide rule that I've seen before include "Obsolete calculator" , "Logs on here" , "Instrument for rapid calculations" , "old computer" , "Old calculating device" .)