Calculation device I'll use, designed to impress friends occasionally around (5,4)
I believe the answer is:
slide rule
'calculation device' is the definition.
(device for making calculations)
'i'll use designed to impress friends occasionally around' is the wordplay.
'designed' indicates an anagram (designed with the letters).
'to impress' indicates putting letters inside (impress can mean enlist or recruit).
'occasionally' means one should take alternating letters.
'around' shows that the letters should be reversed in order.
The alternating letters of 'friends' are 'red'.
'red' written backwards gives 'der'.
'ill'+'use'='illuse'
'illuse' anagrammed gives 'sliule'.
'sliule' placed around 'der' is 'SLIDE-RULE'.
(Other definitions for slide rule that I've seen before include "facilitates calculations" , "Obsolete calculator" , "Old calculating device" , "old computer" , "Logs on here" .)