A radio card lists one radio's fundamental operations and the exact keys that perform each one. Twenty-three cards cover seven makes — Yaesu, Icom, Kenwood, Alinco, Baofeng, Wouxun and Radioddity — and every card answers the same forty-nine questions: how to set squelch, change transmit power, pick a repeater offset, set a CTCSS tone, switch between VFO and memory, start a scan, reset the radio. The keystrokes come from the manufacturer's own manual, read page by page. Where a radio cannot do something, the card greys the row and says N/A, because knowing a set has no APRS is worth as much as knowing which button starts it.

Emergencies hand you unfamiliar equipment. The radio in front of you may be a club loaner, a borrowed mobile, or a handheld somebody pressed on you ten minutes ago, and the one you trained on is at home in a drawer. Under that kind of pressure the operations that defeat people are never the exotic ones. You can hear a repeater perfectly and still fail to open it, because the tone is wrong or the shift sits on simplex. You can transmit for an hour on low power and wonder why nobody answers. Each of those is a two-key fix — buried four levels into a menu whose numbering no two manufacturers agree on.

A manual answers the question you can already phrase, and answers it in ninety pages indexed by the maker's vocabulary. A card inverts that. It is indexed by what you are trying to do, it fits on one screen or one sheet of paper, and it needs no power, no network and no search box. Print it, fold it into the go-box, and the radio you have never touched before becomes a radio you can work in the dark.