Complex sentence: Pascal's calculator was limited by its carry mechanism which forced its wheels to only turn one way, so it could add but, to subtract, the operator had to use of the method of complements which required as many steps as an addition.
Split into simpler sentences: Pascal's calculator was limited by its carry mechanism, which forced its wheels to only turn one way so it could add. To subtract, the operator had to use the method of complements, which required as many steps as an addition.