Carries were a major problem in mechanical calculators as well. For example, the upper section of the Curta had a special bell & gearing to allow carries. The

Carries were a major problem in mechanical calculators as well. For example, the upper section of the Curta had a special bell & gearing to allow carries. The Friden STW - a mechanical behemoth - had a complex set of gears within the moving carriage to allow carries & borrows. Same with Monroe & Marchant mechanical calculators. For electric motor driven calculators, the additional weight of the moving carriage - as well as the gearing - set limits on how fast the machine could add and subtract.