Text and Images Copyright (C) 2006, 2007 Mike Sebastian

Durabrand 828 Graphing Scientific Calculator

In early June, 2006, when I first heard that Walmart was selling a graphing calculator for under $20, I had to get one just to see how they were doing it. It turns out that it is just barely a graphing calculator, with a postage stamp sized 35 by 23 pixel graphing region on the left half of the display. It's closest competitor is the Hewlett-Packard 9G, which sells for around $35, and has a similar display (35 by 23 pixel graphing region) and memory specifications.

Shortly after the Durabrand 828's introduction, it appears a second version was quietly introduced. The old version is labeled "SC828" on the PCB, while the new version is labeled "SC-1376" on the PCB. For more details about the two versions, check out the The Great Durabrand Mystery.

As mentioned above, there are two versions of the Durabrand 828 graphing calculator. With the calculator forensics algorithm, it is easy to distinguish between the two versions.

Forensics result for the old SC-828 version. Evaluation of the forensics algorithm (9.0000296195) revealed that this calculator was a clone of the Citizen SRP-320G. It even had the same arcsin bug as the SRP-320G. (Both calculators do not compute arcsin in degrees, even when in degrees mode, as part of a formula such as the forensics formula. The arcsin step of the forensics algorithm must be computed as "sin^-1 Ans".)

Forensics result for the new SC-1376 version. The forensics algorithm produces a result of 8.999999998078897 - a 16-BCD-digit result.

So, what do you get in a $20 graphing calculator? You get:

• LCD: 35 by 23 pixel graphing, 11 characters (the first 6 character postions overlap the graphing region), plus 3 characters for a scientific notation exponent or program steps remaining.
• 50 key keyboard (including the 4 positions of the 4-way rocker key).
• 26 memories (A-Z), plus an ANS (last answer) memory.
• 400 program steps, divided among up to ten program areas (P0-P9).
• Programming constructs: goto, conditional branching, looping (DSZ, ISZ), 9 levels of subroutines.
• The normal arithmatic functions, common and natural logarithms, trigonometric functions in three angular modes, hyperbolic functions, sexigesimal conversions, polar-rectangular coordinate conversions, binary/octal/hexadecimal support, and single and two variable statistics.
• Formula algebraic logic for entry of calculations.
• 12 BCD digits (old SC-828 version) or 16 BCD digits (new SC-1376 version) of precision.
• Powered by a single CR2032 lithium coin cell, estimated by the manufacturer to provied 350 hours of operation.
• Slip-on cover to protect the display and keyboard when the calculator is not in use.

This calculator also comes with an instruction manual in English and Spanish. Most of the text in the manual appears to be printed in a 4-point font, so it is a little difficult to comfortably read.

Probably my biggest complaint about this calculator is the placement of the SHIFT key (the yellow key in the photos below), which should have been in the upper left corner of the keyboard where the MODE key (the green key in the photos below) is located. However, this is the same key placement as found on its parent, the Citizen SRP-320G.

The Durabrand 828 graphing calculator. Durabrand is a registered trademark of Wal-Mart Stores, Inc. The calculator is imported by World Import Company, Inc. - the same company that imports the LeWORLD brand of calculators. Curiously, the only indication of the brand of the calculator is the Durabrand logo at the upper left of the calculator. The brand name and the model number (seen in the lower right corner of the packaging) are not present anywhere on the calculator.

The Durabrand 828 out of its packaging.

The internal view of the old Durabrand 828. Construction is fairly typical, with the chip protected by a blob of epoxy (chip-on-board), and a heat seal conductor connecting the PCB to the display. Disassembly is extremely easy. The battery cover is held by a single screw, with an additional six screws holding the two halves of the case together. The main PCB is held to the front of the case by six screws.

Here is a comparison of the PCBs between the two versions of the Durabrand 828. The old SC-828 version is to the left, and the new SC-1376 version is to the right.