Field guide / Rule 07 — Math symbols
The keys you press for arithmetic are stand-ins: the letter x for a product, the hyphen for a minus, a slash for a fraction. Real math has its own marks — and one of them is safe enough for a machine to set, while the rest are exactly the kind of guess we refuse to make.
When you write a size or a product — a 4 × 4, 1920 × 1080, a 3 × 5 card — the mark between the numbers is the multiplication sign (×), not the letter x you reach for on the keyboard. They look close, but the real sign is centred, balanced, and reads as arithmetic rather than as a stray consonant dropped between two figures.
This is the one math mark we can set with confidence, because the giveaway is unambiguous: an x wedged between two numbers is never a word and never a variable — it is a product. Everywhere else the x is doing another job, and we leave it be.
A true minus sign (−) is its own character — wider and higher than a hyphen, aligned with the digits. But a hyphen between two numbers is genuinely ambiguous: 3-5 is a range in pages 3-5 and a subtraction in 3-5 = -2, and the text alone can’t tell them apart. So the minus joins the primes on the short list of marks we deliberately do not touch — set it by hand where the arithmetic demands it.
One rule, one safe fix: an x between two numbers becomes a real multiplication sign. The minus, the fraction (1/2 reads as a date just as easily as a half), and every other x are left exactly as you wrote them.
An x between two numbers is a product — set as ×.
Spaced dimensions get the real sign, with the spacing kept.
A variable or a name is never a product — left untouched.
The hex prefix 0x is not multiplication — carefully skipped.
Minus and fraction are ambiguous — set − and ½ by hand.
In short
Use × for a product, − for a minus, and the real fraction glyphs for halves and quarters. We can safely set the multiplication sign — an x between two numbers — and we keep our hands off the minus and the fraction, because there a machine would guess as often as it would help.
Want to see it on your own text? Convert a document and read the cleanup report — every multiplication sign we set is counted there.