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One Card Instead of a Pencil Case: The Physics of a Wallet Drafting Tool

Open your pencil case. Count the casualties: a ruler gone yellow with age, its scale worn down to a rumor. A protractor with the zero mark chipped off. Two set squares — one cracked in your bag back in October, the other vanished in solidarity. And a compass: the only piece of school equipment built from a needle and a lever, which everyone has somehow agreed is fine.

Together this still life weighs about 90–140 grams and occupies a pencil case of its own. The Designer does the same job — and a bit more — in a single anodized aluminum card, 1.5 mm thick, weighing about 17 grams. That's nearly seven times lighter than the set it replaces, and exactly one pencil case fewer in your bag.

01The compass problem

Let's start with the most expensive item in the pencil case — and the most troublesome. A cheap compass has play in its hinge. As you sweep a circle, the direction of force on the legs rotates through 360°, and every quarter-turn the slack shifts from one side of the gap to the other. We ran the numbers: just 1° of angular play on typical legs produces a radius error of up to ±1.7 mm — that's 6% on a 30 mm circle. So a circle from a cheap compass is really a spiral that doesn't always meet itself back at the starting point. Sound familiar?

A circle template works dumber — and is therefore more accurate. A cutout in metal has no hinge, no slack, and no moods. The only error source is the clearance between your pen and the edge of the cutout, about 0.1–0.2 mm, and it stays constant along the whole arc: the circle closes where it began.

There's a bonus that parents and airport security will both appreciate: a template has no needle. At all. A circle with no hole punched through the paper, no puncture in the drawing, and not a single sharp object in a kid's pencil case.

0287 × 54: why not exactly credit-card size

Sharp-eyed owners will notice: the Designer is a millimeter and a half longer than a bank card. That's not a manufacturing tolerance — it's aesthetics, computed on a calculator. The aspect ratio is 87/54 = 1.611. The golden ratio φ = 1.618. Deviation: 0.43% — a proportion the eye reads as "right," and has since the Parthenon. A standard bank card (85.6 × 54) sits 2% away from φ — 4.7 times farther. We build a tool for people who work with geometry; it would be odd if the tool itself ignored geometry.

FIELD SKILLS · 7 TRAINERS The Designer is the drafting half of the family; the field half is trained here Sundial, dual-hemisphere compass, distance ruler, plumb bob, moon-phase dial, tread gauge and the parallel guide — all working in the browser. TRY THE TRAINER →

GOLDEN RATIO

87 / 54 = 1.611 · φ = 1.618 · deviation 0.43%

DESIGNER 87×54 · 0.43% FROM φ

ISO BANK CARD 85.6×54 · 1.99% FROM φ · 4.7× FARTHER

In practice that extra 1.4 mm changes almost nothing: the card slides into leather wallet slots, notebook covers and pockets exactly as before. The one honest exception — rigid machined cardholders with trays milled strictly to the ISO 85.6 mm boundary: there the Designer will sit proud or not seat at all, so if your carry is an aluminium tray, check its tolerance first. But now you know you're holding a rectangle whose proportions were argued over by ancient architects. A small thing. But ours.

And since we're being concrete, the full working set on the plate: 80 mm metric and 3″ imperial rulers with through-cut ticks, L-squares in both systems, a 0–180° protractor with a slotted precision arc and a radian mark at 57.3°, quick angles at 30/45/60°, circle templates ø6–12 mm and ø1/4–1/2″, compass pivot holes in both systems, parallel-line notches, pica scales — and pixel rulers cut for 350 and 150 PPI print proofs, so what you check on paper is the density the file will actually print at. The phone stand works A-frame style: slide any bank card into the slot, the two plates lean into a tent with a ledge, and the phone rests on it — it holds an iPhone Pro Max, so a reference photo stays upright next to the sketchbook regardless of what you carry. One drafting note: at 1.5 mm plate thickness the small-radius templates want a 0.3–0.5 mm mechanical pencil or a fineliner — a cone-shoulder wooden pencil rides the rim before the lead reaches paper.

03Anodizing is not paint

The Designer's colors — Classic Black, Yellow, Survival Orange, Burgundy Red, Ocean Blue and Cherry Violet — look like a design decision. Technically, they're a side effect of an engineering one.

Anodizing is the electrochemical growth of an Al₂O₃ oxide layer straight out of the metal's surface. The dye sits inside the pores of that layer, not on top of it — so the "paint" has nothing to peel from, because it lives inside ceramic. The layer itself is harder than the metal beneath it: roughly 200–400 HV versus ~95–110 HV for the 6061 base alloy. The scale, laser-engraved through that layer, stays crisp and doesn't wear off under fingers — unlike the printed markings on plastic rulers, which surrender a little more each semester.

The colors also serve a plainly practical purpose: a bright card is visible on a desk full of paper. A transparent ruler is an object evolutionarily optimized for disappearing; an orange aluminum card has been denied that talent.

04Legal everywhere. That's a spec, not a compromise

The Designer has zero blades and zero sharp points. It's a card with a complete list of "allowed":

School — not one feature that could raise a question. A needle-tipped compass is already a gray zone in many schools; a circle template isn't.

Flights — no blade, no point — and the final call still belongs to the officer at the checkpoint. See what actually flies.

Office, courthouse, stadium, concert — anywhere with a metal detector, the Designer walks through as exactly what it is: a drafting instrument.

We also make cards with blades — and we state plainly where you can't carry those. The Designer is the opposite pole of the catalog: a tool with simply no carry restrictions.

0515 tools for people who think with a pen in hand

The full loadout — 15 functions in one plate:

Metric + Imperial rulers — a full face of the card for each system (details below), because our customers live in both.

Protractors in degrees and radians — angles for logos, layouts and joinery; the radian scale is a quiet salute to everyone who remembers what π/6 means.

L-squares — check a right angle faster than you could explain why. Compass guides — for arcs where a template isn't enough. Circle templates — circles without a needle and without hinge slack.

Angle markers 30° / 45° / 60° — three angles that cover 90% of layouts. Isometric grids & guides — a quick 3D sketch on a café napkin when the idea arrives and the tablet stayed home.

Pica & pixel scales — for those who do layout and know why an inch divides into 6 picas.

See every scale in 3D → Tool Explorer

This is a first-sketch instrument. Not a replacement for a drafting table or CAD — but the object that's on you at the exact moment an idea needs pinning down before it escapes.

06Two faces — two measurement systems

The Designer is bilingual: one face of the card is fully imperial, the other fully metric. This is not an inch scale squeezed onto the edge as an afterthought — it's two mirrored instruments on one plate. Working with an American client — inches, picas and fractions; with the rest of the world — millimeters. Switching systems means flipping the card, which is still faster than multiplying by 25.4 in your head without an error.

And for those who design screens: pica & pixel scales. Print the mockup, lay the card on it — and measure the interface in the units it was actually built in, not "roughly in centimeters." Typographers measured in picas for centuries before pixels existed; we put both eras on one edge of the card.

07A phone stand made of two cards

The center cutout is a slot for a regular bank card. Insert one — and the assembly becomes a smartphone stand: zero extra parts, zero hinges to wear loose, and the whole structure builds itself from the contents of any wallet on the planet. Reference image in view, tutorial playing, both hands free for the pencil. We built a tool that uses another card as a spare part — and we consider it the most productive use of a credit card there is.

08Material, colors, and the set

Aluminum 6061 here is not a cost cut — it's the correct answer to this class of problems. Titanium wouldn't add accuracy to a single scale; it would only add weight to your wallet. A drafting tool needs in-plane stiffness (check: 1.5 mm doesn't bend inside a wallet), a stable scale (check: laser over anodizing), and low mass (check: ~17 g). Everything beyond that is showing off — and we've reserved the showing off for our titanium cards, where it belongs.

Yellow — the brightest of the six, and the one you'll find first if it slides under the couch. Classic Black — goes with everything and asks for no attention. Survival Orange — signal-grade; visible on a desk, in grass, and at the bottom of a bag.

Burgundy Red — a deep wine red, for people to whom "red" doesn't mean "fire truck". Ocean Blue — a saturated blue; yes, we thought about blueprint ink too.

Cherry Violet — the newest in the palette: dark cherry with a violet undertone.

And for those who find choosing hard, the colors come together as a set — a collection that looks like a limited art drop and works like a full kit of instruments: for a studio team, a classroom, or simply to fan out on a desk and feel like the curator of your own small exhibition. Bohemians welcome. It's an easy gift for a student — and one you won't hesitate to hand an architect with twenty years behind them.

May the only spiral in your notebook be the one you drew on purpose. The Card Finder narrows twenty cards to yours in four questions, about 30 seconds.

Andrii Gurskyi, founder & engineer, MRF.Tools