speeds proportional to the digit in that column. This meant that the machine contained, in all, several hundred individual gears. Carries from lower-order digits came in via one planetary differential per dial. If one held down the + bar, in neighboring columns to the left (with zeros for them in the keyboard), one could see two or maybe three higher-order dials moving at the speeds one would expect. Watthour meter dials, like the hour hand of a clock, make no attempt to point to the correct digit, if the dial to the right is between, for example, 3 and 7, or so. Such misalignment would be intolerable in a calculator's dials, so each of the Marchant's dials had a constant-lead ("snail") cam attached. Omitting important details, this cam determined the amount of movement needed to realign the result dials. That correction was applied by a second spur-gear differential, again, one per dial. Some calculators that had been serviced had dials that were mispositioned by (probably) 3.6 degrees; the gears weren't quite meshed correctly when reassembled. The calculator was very complicated compared to, for example the Friden STW, a machine notable for its relative internal simplicity. Much of the Marchant's control mechanism was beneath the keys, and had about 25 "layers" of levers, linkages, latches, and such. It had three driveshafts, extending across the mechanism. Most other calculators had only one. Most mechanical calculators capable of fully automatic division (and there were many), subtracted until the accumulator went into overdraft ("subtracted one time too many"), then added once to restore the value in the accumulator. The Marchant, however, contained a chain of analog comparators to anticipate the overdraft, and prepare for the next quotient digit. The Marchant mechanism, internally, differed profoundly in many respects from other makes of calculators of the same general variety. By virtue of sophistication (and complexity), it gained a considerable speed advantage, compared to other designs. External links SCM Marchant Cogito 240SR calculator Stanley Frankel, Recirculating Memory Timing, filed February, 1964, issued June, 1970 Marchant Figurematic calculator Detailed technical description, with numerous photographs, by an engineer Mechanical calculator companies Electromechanical calculator companies Defunct computer companies of the United States Defunct companies based in California