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contex_b [2020/09/07 15:38]
clodoveu
contex_b [2023/01/03 19:13] (current)
clodoveu
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Curiously, all keys in the same column move when a key is pressed. Key arms are arranged as a fan, and when you press the 5 key, the fan closes and drags down the other 4 key arms in the same column. The reset mechanism is also curious: digits go to 9 when the reset button is pressed down, and 1 is added when it is released. The mechanism is too simple to include any kind of functional locking or safety features: unskilled operators easily make input mistakes, by not depressing a key to the very bottom, or cause carry errors when releasing the keys. As in the case of Comptometers and Burroughs, its most efficient operation requires pressing keys in multiple columns at the same time, instead of touch-typing each digit in turn. Adding columns of numbers can be done column-wise,​ giving the same result. Say you need to add 123 + 456 + 789. You can type in 3 - (3+3) - (4+5) on the rightmost column, then 2 - 5 - (4+4) on the second, and 1 - 4 - (4+3) on the third, much like adding manually. Curiously, all keys in the same column move when a key is pressed. Key arms are arranged as a fan, and when you press the 5 key, the fan closes and drags down the other 4 key arms in the same column. The reset mechanism is also curious: digits go to 9 when the reset button is pressed down, and 1 is added when it is released. The mechanism is too simple to include any kind of functional locking or safety features: unskilled operators easily make input mistakes, by not depressing a key to the very bottom, or cause carry errors when releasing the keys. As in the case of Comptometers and Burroughs, its most efficient operation requires pressing keys in multiple columns at the same time, instead of touch-typing each digit in turn. Adding columns of numbers can be done column-wise,​ giving the same result. Say you need to add 123 + 456 + 789. You can type in 3 - (3+3) - (4+5) on the rightmost column, then 2 - 5 - (4+4) on the second, and 1 - 4 - (4+3) on the third, much like adding manually.

-Subtracting in the Class is, as in the Comptometer, ​also troublesome. The operator is required to enter a tens-complement number, using preceding 9s and typing the number to be subtracted by looking at the small numbers on the keycaps. The preceding 9s are actually zeroes if you look at the small numbers in the keycaps. Oh, and the subtrahend must be reduced ​by one so the tens-complement works correctly. Whew. More on Burroughs Class 5 operation [[http://public.beuth-hochschule.de/​hamann/​burroughs/​burro5/​index.html|here]].+Subtracting in the Class is, as in the Burroughs Class 5 and in the Comptometer,​ troublesome. The operator is required to enter a tens-complement number, using preceding 9s and typing the number to be subtracted by looking at the small numbers on the keycaps ​-- only the Contex does not show the complements on the keycaps. Oh, and the subtrahend must be incremented ​by one so the tens-complement works correctly. Whew. An example345 - 123Tens-complement of 123: 876; adding one, 877Enter 345 in the machine, then 999877Result (ignore the first one): 000222.

-There was practically nothing to do in this machine. Its three rubber feet were deteriorated,​ but I was able to replace them with round hydraulic seals, after making a countersinked hole in each one. After a general cleaning, I now only mean to restore the front Contex logo, which is all but invisible, as in the case of many units whose photos can be found online. The case has the makings ​of a lost handle, which I also plan to replace.+More on Burroughs Class 5 operation [[http://​public.beuth-hochschule.de/​hamann/​burroughs/​burro5/​index.html|here]]. The same principles appy to all Comptometer-style machines.
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+There was practically nothing to do in this machine. Its three rubber feet were deteriorated,​ but I was able to replace them with round hydraulic seals, after making a countersinked hole in each one. Years later, in 2023, I replaced these feet with 3D-printed ones, using flexible filament. After a general cleaning, I now only mean to restore the front Contex logo, which is all but invisible, as in the case of many units whose photos can be found online. The case has the markings ​of a lost handle, which I also plan to replace.

**Have a mechanical calculator stored somewhere, and want to get rid of it? Send it to me!** **Have a mechanical calculator stored somewhere, and want to get rid of it? Send it to me!**
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{{ http://​www.dcc.ufmg.br/​~clodoveu/​files/​Images/​Contex-model-B/​20200823 as purchased.png?​500 | As purchased}} {{ http://​www.dcc.ufmg.br/​~clodoveu/​files/​Images/​Contex-model-B/​20200823 as purchased.png?​500 | As purchased}}

+After cleaning

+{{ http://​www.dcc.ufmg.br/​~clodoveu/​files/​Images/​Contex-model-B/​contex-1.jpg?​500 | Contex model B}}

-[[http://www.johnwolff.id.au/calculators/Burroughs/Burroughs.htm John Wolff shows a wider Class 5with 13 columns instead of 9, including ​column for Sterling currency units]]+{{ http://www.dcc.ufmg.br/~clodoveu/files/Images/​Contex-model-B/​contex-2.jpg?​500 ​Contex model B}}
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+Inside view
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+{{ http://​www.dcc.ufmg.br/​~clodoveu/​files/​Images/​Contex-model-B/​contex-3.png?​500 | Contex model B}}
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+Bottom view -- notice the five blades for the keys in each columnarranged as fan
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+{{ http://​www.dcc.ufmg.br/​~clodoveu/​files/​Images/​Contex-model-B/​contex-4.png?​500 | Contex model B}}
+