Odhner

Specification

• Original Odhner Arithmos pinwheel calculator (estimated from the 1920's)
• 9 decimals input
• 13 decimals accumulator
• 8 decimals register

Origin

Donated in 2013.

Condition

Generally works, but:

• if the first decimal of the register contains a 1, it can't be reset to 0. Not that much of a problem, you can subtract 0 while the carriage is on the first digit to set it to 0.
• Mechanics needs some cleaning an maybe a little lubrification but I don't want to fiddle with it as I don't have experience with restoring this kind of apparatus.
• a lot of the digits have lost their paint.
• there seems to be a part missing to shift the carriage. there are some holes and pictures of similar models show buttons to advance the carriage by one position left or right.

Usage Hints

• Input is given by setting the 9 levers.
• The right hand counter is the accumulator. It stores the result of the addition or subtraction.
• The left hand counter is the register. It counts the number of turns.
• Input is transferred to the accumulator by turning the crank, clockwise turn for addition, counter-clockwise for subtraction.
• The carriage can be shifted to align the input with a certain decimal of the accumulator and the register.
• Both register and accumulator have a reset handle, give it a full turn to set all digits to zero.
• The input can be easily reset by pulling the reset handle left while turning the crank until it pushes all levers to zero.
• (other than the above) always turn the crank a full turn. You can always undo a turn by turning in the opposite direction.
• A bell signals an overflow condition.

Addition

• Reset accumulator
• Input the first operand.
• Turn clockwise.
• Input the second operand.
• Turn clockwise.
• Read result from accumulator.

Subtraction

• Reset accumulator
• Input the first operand.
• Turn clockwise.
• Input the second operand.
• Turn counter-clockwise.
• Read result from accumulator.

Multiplication

• Reset accumulator and register.
• Shift carriage all the way to the left.
• Input the first factor.
• Turn clockwise as many times until the last decimal in the register equals the last digit of the second factor.
• Shift the carriage 1 position to the right.
• Turn clockwise as many times until the fore-last decimal in the register equals the fore-last digit of the second factor.
• Repeat the last two steps for all digits of the second factor.
• Read the product from the accumulator.

Division

• Reset accumulator
• Shift carriage to the right, allowing space for decimals.
• Input the dividend.
• Turn clockwise to transfer it to the accumulator.
• Reset the register.
• Input the divisor.
• Shift carriage to align the leading digits of input and accumulator.
• Keep turning counter-clockwise until the bell rings.
• Turn clockwise to undo the last turn.
• If accumulator contains all zeros, read exact quotient from register, else shift carriage one position left and repeat last two steps.
• If not dividable, the process stops when the carriage is all the way to the left. Read approximate quotient from the register and remainder from the accumulator.

Square root

• Reset accumulator
• Shift carriage all the way to the right.
• Input number
• Turn clockwise to transfer it to the accumulator
• Reset register
• Shift carriage aligning left-most digit of input with left-most digit of the value in the accumulator
• Set a 1 in the input that is aligned with the right-most digit of the value in the accumulator and turn counter-clockwise
• Set the next odd number (3) and turn counter-clockwise
• Repeat with next odd numbers (5, 7, 9, 11, 13, ...) until the bell rings.
• Undo last turn by turning clockwise.
• Subtract 1 from input
• set a 1 in the next input digit (one decimal to the right)
• shift carriage left.
• repeat the process of subtracting odd numbers until the bell rings.
• If accumulator contains all zeros, read exact result from register
• If carriage reaches left-most position, read approximate result from register