What does the cryptic crossword clue "Calculating type’s more pathetic when losing head (5)" mean?

The definition is "head". The wordplay uses a deletion. ADDER (deletion) = ADDER; definition: "Calculating type's" The answer is ADDER.

Calculating type’s more pathetic when losing head (5)

Guardian Cryptic #29437 | 7 Down | 2024-07-17 flower