The keyboard of the Compet 16 is laid out in a very traditional fashion, with four groupings of keys. The key caps are of very high-quality molded plastic, featuring molded-in nomenclature. The left-most group of keys contains the constant key, and the [CE] (Clear Entry), and [C] (Clear) keys. The [CE] key clears the content of the entry register, allowing entry errors to be corrected. The [C] key clears the working registers of the calculator (it does not clear the memory register), and also unlocks the machine when an overflow occurs. The next grouping of keys is the traditional numeric keypad, with a double-width zero key. The numeric entry keys feature a mechanical interlock that prevents the depression of more than one key at a time. Such a feature is good from the point of view of minimizing entry errors, but at the same time can actually slow down a skilled user, as each key must be completely released before the next key can be pressed. Later calculators abandoned the mechanical methods and used electronic means to avoid entry errors caused by inadvertent depression of multiple keys at the same time.
The math function keys make up the next group, with lighted [X] and [÷] keys. These keys have a molded-in red-colored jeweled nomenclature, with incandescent lamps mounted beneath the key that light when a multiply or divide operation is pending. The white [=] key serves as the addition function key, and also triggers the machine to calculate the result of multiplication and division operations. The red [=] key is used for subtraction. The [RC] key swaps the content of the entry and operand registers. The right-most group of keys controls the operation of the memory register. The [CM] key clears the memory register, extinguishing the memory annunciator on the display panel. The [MR] key pulls the content of the memory register into the display. The [M-] and [M+] keys subtract or add the current content of the display to the memory accumulator register. If the memory add or subtract operation results in an overflow, the machine goes into overflow condition, but the memory register retains its previous content.