Think calculatingly? (6)
I believe the answer is:
reckon
'think' is the definition.
(synonyms)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for reckon that I've seen before include "Calculate, be of the opinion" , "what people who count will do" , "Calculate roughly" , "Calculate, compute or estimate" , "Consider or calculate" .)