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Matthew Lim’s PW-03 is a hand-cranked, six-digit mechanical calculator that performs addition, subtraction, multiplication, and division without electronics or motors. CircuitDigest reports that it uses more than 130 custom-designed parts; its pinwheel input, accumulator, and rotation counter turn the operator’s crank movements into arithmetic.
What the PW-03 does
The PW-03 combines four adjustable input pinwheels with a six-digit accumulator and a rotation counter, according to CircuitDigest’s report. Lim’s project listing independently describes a pinwheel input, six-digit accumulator, rotation counter, and two handles. All operations are hand-driven, with no electronics or motors, the creator says.
The machine supports addition and subtraction directly, while multiplication and division use repeated operations. Its mechanical approach makes the operator part of the calculation: setting digits and turning the crank determine how values move through the mechanism.
How its pinwheels and crank perform arithmetic
Addition and subtraction
To enter a value, the operator sets movable pins on the pinwheel from 0 to 9, then turns the crank to add that value to the accumulator display. Turning the crank in the opposite direction performs subtraction. These operating details are described by CircuitDigest.
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Multiplication
The report describes multiplication as repeated addition. The operator adds the entered value multiple times, repositioning the pinwheel assembly by decimal place as needed. That repositioning lets the mechanism account for the different place values in a product.
Division
Division uses repeated subtraction: the entered divisor is subtracted from the accumulated value, and the rotation counter records the quotient. The accumulator display retains the remainder when the operation is complete, according to CircuitDigest.
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What went into the mechanism
CircuitDigest reports that the PW-03 has more than 130 custom-designed parts and that Lim tried more than 30 versions of the carry mechanism. The report says the design was revised to use ball springs and smoother moving surfaces to improve motion through the carry system.
The same account says high-precision resin printing helped with small moving pins that could catch on FDM print layer lines. It also describes tough resin for parts that flex repeatedly or transmit force. These are details of the development described in that report; Lim’s separate project listing provides a filament-based reference build, so the two material descriptions should not be treated as one universal recipe.
Rank #3
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What a listed build requires
Lim’s project listing characterizes the build as difficult and tolerance-sensitive. It calls for a well-calibrated printer with at least a 180 × 180 mm build area and about 450 g of filament in two colours; the listing says basic PLA works. Those figures are the creator’s listed requirements, not a guarantee that every printer or slicer will produce the same fit.
Creator-listed print settings
The listing describes a reference build printed on a Bambu Lab P2S and a Bambu Lab A1. Its recommended settings are:
Rank #4
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- 0.12 mm layer height for precision parts
- 0.16 mm layer height for other parts
- 0.20 mm layer height for the outer cover
- Three walls and 15% cross-hatch infill
These are project-specific settings from the creator’s listing, rather than universal recommendations for other printers or slicers.
Listed hardware
The project listing specifies the following external hardware:
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- Mechanical Switch Key Feel for Enhanced Typing: Imitates the feel of a mechanical keyboard for fast and accurate input; tactile feedback and a distinct clicking sound make calculations satisfying. Large buttons and ergonomic spacing prevent hand fatigue.
- Dual Power for Long Battery Life: Operates with both solar and battery power for continuous use, featuring an auto power-off function that activates after 6 minutes of inactivity to extend battery life. Compact, lightweight, and powered by a single AAA battery (included), this calculator is perfect for quick calculations at home, school, or the office.
- Lovely Retro Design: Typewriter-style round keys and a vintage aesthetic add a classic charm to any workspace. Ergonomically designed keycaps and a spring-loaded mechanism protect wrists and allow for comfortable typing with both hands, making it suitable for both desktop and handheld use.
- Large, Easy-to-Read LCD Display: Features a 12-digit extra-large 5” LCD screen with a vertical back, angled at 15° for optimal visibility. Ensures that numbers are easy and better to read, making it perfect for detailed budgeting, schoolwork, and office tasks.
- Durability with Anti-Slip Stability: Crafted from high-quality ABS material for long-lasting durability. Equipped with anti-slip foot pads that add extra friction to keep the calculator stable on any surface, ensuring ease of use during fast calculations without slipping.
| Part | Quantity |
|---|---|
| M2 × 4 mm screws | 46 |
| M2 × 6 mm screws | 42 |
| M2 × 14 mm screws | 5 |
| M2 × 20 mm screws | 2 |
| 3 × 4 mm ball spring plungers | 15 |
| 5 × 2 mm magnets | 10 |
For the plungers, the creator specifically names the Bambu Lab Smooth Ball Spring Plunger and warns that alternatives with similar stated dimensions may differ slightly and fail to seat correctly. The listing is the appropriate place to check current file access, guide details, and licence terms before building: Matthew Lim’s PW-03 project listing.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.How the design fits into calculator history
CircuitDigest connects the project’s inspiration to historic mechanical calculators, especially the pinwheel mechanism associated with Willgodt Odhner. A specialist calculator reference likewise describes the Odhner Arithmometer as a pinwheel-mechanism calculator. That is useful context for the mechanism, but does not establish that the PW-03 reproduces a particular historical model. Odhner Arithmometer reference
What is—and is not—established about performance
The available accounts describe the PW-03’s design, operating method, and a creator-listed build specification. They do not establish independent accuracy testing across a test suite, reliability over extended use, or build success rates among other users. The reported digit capacity and operations describe what the project is designed to do, not comparative performance measurements.
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