All functions are working. All tubes are working as seen in the photos. I'm sure if you are looking at this listing, you are aware of the functions, but I've noted them below.

The CS-16 is a 12-digit, fixed decimal, four function calculator with accumulating memory register. The machine provides a constant function for multiplication and division, with a push-on/ push-off keyboard key labeled [K] to enable the function. It follows Sharp's consistent design of using arithmetic logic for addition/subtraction, and algebraic input for multiplication and division. The machine provides fixed decimal point selections, via a rotary switch on the keyboard panel, of 0, 2, 3, 4, and 6 digits behind the decimal point. Two different settings are available for each selection, one which causes truncation, and the other rounding off to the selected decimal position. Strangely, an additional (blank) selection is available on the decimal point setting switch. Placing the switch in this position results in an immediate input overflow upon trying to operate on any number entered. Why Sharp did this is unclear, as it surely ended up being the source of confusion when users inadvertently set the decimal point selection switch to this position. Numbers may be entered with up to seven digits behind the decimal point, with any digits in excess of the decimal point setting of the machine being discarded when the number is operated upon. Attempting to enter more than seven digits behind the decimal will cause an input overflow.

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.