Marchant

Marchant XLA

Set a number on the "keyboard" by adjusting the red and white levers. Now turn the big crank at right one direction to add and the other to subtract. The keyboard digits are added/subtracted into the digits of the accumulator right below them. At the same time, the counter at left is incremented/decremented by 1 in the position corresponding to the white arrow. With this you can readily do multiplication and division too.

This is a wonderfully preserved calculator in great working order after disassembly and a thorough cleaning. Shiny and unworn, it's a survivor from the early 20th century.

Marchant ACR 8M

This sturdy motorized calculator was built for speed using a proportional gear mechanism. Given its serial number, it was made in 1946 according to http://www.vintagecalculators.com/html/marchant.html

It was given to me by my friend Paul, who says it was an off-to-college gift from his grandparents to his father.

The calculator has a lowest register of dials that just shows what has been entered on the keyboard. The lower register on the carriage is an accumulator, and the upper register is an operation counter.

Pressing + adds the number in the keyboard register into the accumulator register and increments the counter register by 1 in the position marked by the red arrow on the upper cowling. Pressing - performs the reverse operation. Note that the carriage can be moved left and right (via the black arrow keys at the right side) so addition and subtraction can be performed into whatever positions of the accumulator the operator wants. The carriage moves in the direction of the arrow.

The black keys and the green arrow keys are used to do multiplication. Pressing a black key adds the keyboard register into the accumulator the number of times represented on the key, increments the counter (at the red arrow) by the number on the key, and then shifts the carriage left or right according to which green arrow key is pressed. (Pressing the one pops the other. If the red No Shift key is pressed, no shift occurs.) So if you want to multiply 456 x 123, you start by entering 456 on the keyboard. If the left-arrow green button is down, you then press the black buttons in order 1,2,3. Alternatively, of the right-arrow green button is down, you press the black keys in order 3,2,1.

If you press the red Reverse key before pressing a black button, the number in the keyboard register is subtracted from the accumulator the number of times represented on the black button.

Division works by entering the dividend into the keyboard and then pressing + to transfer it into the (cleared) accumulator. Then you enter the divisor into the keyboard and press the red Auto Divide button. The machine will then repeatedly subtract the keyboard register from the accumulator, shift the carriage left when the value in the accumulator falls below the value in the keyboard register, and repeat until the carriage has moved fully leftward. During division, the keys are locked, and if you want to abort you can press the red Stop button. (For some reason it seems to require 2 presses of the stop button to halt a division.)

The little black buttons on the carriage can be used to set a decimal position - really a tab stop on the carriage. The green Clear Return key will restore the carriage to the tab stop position after an operation. (If the little red switch to the right of the + key is in the down position, a carriage return is automatically performed at the end of a calculation.) If the carriage is already at the designated tab stop and you press Clear Return, the carriage will go all the way to the end in the direction of the depressed green arrow key.

Oddly, the green Clear Return key doesn't clear anything. (It could be that something is broken. I opened the machine and looked but didn't seen any obvious problem.) Instead the two red Middle Dial and Upper Dial keys below it do the clearing, and you can press them at the same time. On this machine, someone has reversed the keycaps on these two keys, such that pressing Middle Dial clears the upper dial and vice versa.

The red Key Board Dial key clears the keyboard register and pops all the keyboard keys. The little red keys below a column clear that column only. There's a small lever below and to the right of the Key Board Dial key that can be flipped leftward to lock the key and prevent it from being pressed. It's not clear to my why anyone would want to do that.

The machine has several sliders to set decimal positions. In addition is has flat rods between the keyboard columns. One side is brown as shown in the picture, and the other is white. You can flip them over to partition the keyboard columns in some way other than the green/yellow coloring suggests.

Finally, there's a small switch to the right of the 9 multiplier key. Flipping it down reverses the effect of addition and subtraction on the counter. I.e. normally each addition will increment the counter by 1 (in the position of the red arrow) and each subtraction will decrement it by 1. Flipping the switch down causes the counter to decrement on addition and increment on subtraction. This would be a useful switch if you were doing division by manually driven repeated subtraction (the way you would on a Curta) but given that this machine automates division I can't see what purpose this switch serves.

Altogether, this is a pretty nice device. It weighs about 30 pounds and makes a great and wonderful commotion when in the throes of a division! If you were in an office full of these, your ears would ring so much you might not notice the quitting time whistle.