each decade where the keys latch when pressed, with interlocking which prevented more than one key in any decade from being latched. The latching allowed the operator to quickly check that the correct number had been entered before pulling the operating lever. The numbers entered and the final total were printed on a roll of paper at the rear, so there was no danger of the operator writing down the wrong answer and there was a copy of the calculation which could be checked later if necessary.

The Class 2 machine, called the "duplex" and