The Craig 4505 calculator, introduced in 1973, is a well-built device from the early era of electronic calculators. Manufactured by the Craig Corporation in Compton, California, and made in Japan, this calculator features a horizontal format with a sturdy two-piece case made of black patterned plastic. The design includes gently rounded top and bottom edges, giving it a quality feel. The display is housed in a raised, slightly tilted section on the left, with a neutral plastic filter that provides a clear image. The keys offer long travel and a springy feel, producing a prominent musical click upon return.
The calculator is powered by 6V DC, requiring four AA batteries. It also accepts an adaptor/charger (Craig 9227, 6V DC center negative) through a socket on the top side. Rechargeable batteries can be charged even when the calculator is off, with a quoted charge time of 24 hours. A low battery indication is provided by all decimal points lighting up.
The display features an 8-digit blue Vacuum Fluorescent Display (VFD) with a ninth digit for negative and overflow indication. An additional single red LED indicates memory usage. The calculator offers standard functions including addition, subtraction, multiplication, division, and percentages, along with a two-function memory. It also includes switched auto-memory and fixed decimal modes, and operates on semi-Reverse Polish Notation (RPN) logic.
The original case for the Craig 4505 is made of soft black plastic with a zip that covers one-fifth of the side, the top, and four-fifths of the other side. It features silver printed “Craig” branding on the front and includes a black plastic carry strap. This calculator appears to be a later clone of the Telatronic SM8.
The internal components of the Craig 4505 include:
- 1 CPU: Rockwell 15330OC 7324 (date code week 24 of 1973)
- 1 8-digit plus “E” digit VFD; single tube round face
- 6 transistors
- 15 diodes (8 on the main board, 7 on the keyboard)
- 7 capacitors
- 21 resistors
- 1 variable resistor
- 2 rectifiers: KD-214S 3FG (date code June 1973)
- 1 transformer with a mini board for power components
The keyboard assembly (B 013211) is attached to the front of the case with five screws, while the main board (SM-003-D) sits in the rear, held by four plastic pillars and glued in place. The two are connected by 14 flying wires. To access the interior, remove the screw from the rear, and the back will lift off, hinging at the bottom to preserve the link cables.
Logic:
- The (C) button clears the last entry of a number on the first press and clears the entire calculator on the second press.
- Overflow on number input is suppressed; typing a ninth digit is ignored.
- An overflow shows the result and “C” (or “E” if negative) in the far left (ninth) digit and is recoverable using (C).
- Divide by zero shows zero and “C” in the far left (ninth) digit and is recoverable using (C).
- The logic is semi-Reverse Polish Notation: to perform 3-4, key in (3)(+)(4)(-).
- Automatic constant on multiply and divide (first entry for multiplication, second for division, and last entry for addition or subtraction).
- Negative numbers are shown with a “-” in the far left (ninth) digit, allowing full eight-digit negative numbers.
- The percentage function can mark up or down: to take 5% off 50, key in (5)(0)(X)(5)(%)(-) to get “47.5”.
- Switched floating decimal mode [AF], fixed two-digit mode [2], and financial input mode [A2]. The latter causes the input of (1)(2)(3) to become “1.23”.
- It has the pseudo fixed decimal bug: key in (1)(+)(.)(0)(0)(0)(+) to get “1.000”, which remains a fixed three-digit decimal number until more digits are needed or multiply/divide is used.
- The memory is switched on, and every press of (=) or (%) accumulates to memory.
- Memory store is indicated with the individual red LED.
The main board sits deep down to the side of the battery compartment. Typical early calculator with loads of components, many of which, like the power transistor in the middle and the large rectifiers, are a bit of an overkill for the power hungry vacuum fluorescent display. Notice that the have cut out a hole for the main IC which is mounted from beneath with the legs bent horizontally. The two bunches of wires at the bottom connect to the keyboard assembly.
The Craig 4505 calculator is a basic calculator from the early 1970s, featuring a clear VFD display and a range of standard functions. Its semi-RPN logic and fixed decimal modes make it a versatile tool for basic calculations, although it has some limitations due to its archaic input method and a pseudo decimal bug.
