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Calculators: Handheld: Datacal II

Size (approx):

77mm x 125mm x 24mm(max)  (w,h,d)
Weight 98g excluding batteries

Power:

6V DC, 4 x N size batteries, 75mA.  It accepts an adaptor (undefined but 5mm plug, centre negative) through a socket on the right side in line with the (=) key. The battery life is quoted as 20 continuous hours.
Case: Quite unique compact style made from a two-piece matt white plastic case.  White and burgundy colour scheme is matched well by the small logo plate that sits in its own recess.  The red display filter is tilted at about 20 degrees so it works well on the desk as well as in the hand and gives a nice bright display.  The on switch label is raised but unprinted.  The keys are soft-click short-travel type and work very well.  They are also slightly tilted as well as horizontally concave.
Display: 8 digit red LED with bubble lens and no ninth digit
Features: Standard four functions, percentages and averages
Age: 1974/5
Manufacturer: No manufacturer's name but the back panel states V.I.P Programs Co., 113 Rushmore St., Westbury, N.Y. 11590.  Serial No. 400-112126.
Comments:

 

I believe this was made by Corvus (consumer division of Mostek) as it looks exactly like the Corvus 400 of c1974 (and the Radio Shack EC-230 of 1976).  Lovely compact design with a strange "N" key for averages.  Good logic only let down by seven digit negative numbers and lack of error recovery.

Components:

1 x cpu: Mostek MK5026(?)0N ASSB Malaysia 7451 L (week code 51 of 1974) 28 pin DIL, 0.6" width
2 x ICs: ITT 501-5N 7409, 14 pin DIL, 0.3" width (possibly display drivers)
1 x 8 digit LED display unit with bubble lens (HP dated 7443)
1 x diode
2 x capacitors
1 x resistors
1 x transformer; Mostek DC-10 1013

Boards: The keyboard assembly (ref KB3139 5015) is attached to the front via 9 plastic lugs.  It is joined to the main cpu board by a 15-way ribbon cable.  The main cpu board sits on six plastic posts.
Construction: Remove the two screws from the back and gently separate by hinging off the bottom two lugs.  Be careful it will be easy to damage and the top rear section is very thin. If in any doubt don't do it.

Logic comments: (C) cancels an incorrect numerical entry on the first press and clears the calculator on the second so it is a CE/C key really
There is automatic constant on all four functions
Input overflow is not suppressed, inputting a ninth digit causes an overflow which is not recoverable
Negative sign is shown in the immediate left hand digit but as there is no ninth digit you are limited to seven digit negative numbers 
Divide by zero shows a flashing "0" and is not recoverable
Overflow is shown by a flashing result and is not recoverable
The (N) key is used for averages; to find the average of 3,4 and 5 key in (3)(+)(4)(+)(5)(/)(N)(=) and it displays "4".  The (N) key retrieves the number of numbers you have added in a chain.
Percentage key just divides the current number by 100

box

Considering how nice the calculator is - you couldn't get duller than this!   The box measures 110mm x 190mm and is 40mm deep.  It is made of quite stiff white card with a full pull-off front half.  There is one solitary blue sticker on the front and nothing else.  Why blue?

Inside is a complex-fold tray that holds the calculator with a foam protective piece.

manual

That's better, at least the manual matches!    It measures 88mm x 140mm with a burgundy and yellow printed cover and black pages inside.  It has 18 printed pages in total, two off which are a tear off warranty card with perforations.

It has quite a few clear examples and a lot of descriptive text with a good diagram of the calculator keys.

It has a date of purchase (which matches the serial number of this example) of 21 February 1975.

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