Slip by government calculator (5,4)
I believe the answer is:
slide rule
'calculator' is the definition.
(I've seen this before)
'slip by government' is the wordplay.
'slip' becomes 'slide' (synonyms).
'by' says to put letters next to each other.
'government' becomes 'rule' (rule can mean government or control).
'slide'+'rule'='SLIDE-RULE'
(Other definitions for slide rule that I've seen before include "Obsolete calculator" , "Logs on here" , "facilitates calculations" , "Old calculating device" , "Instrument for rapid calculations" .)