What ′ means
Read the expression, not the stroke alone. An arcminute is a subdivision of a degree in angle measurements. A derivative describes how a function changes; the prime follows the function’s name.
Prime notation for derivatives appeared in print by 1749—not necessarily the stroke’s invention.
Don't confuse it with
1Combination ideas
3The first derivative of f, evaluated at x.
Five feet, nine inches.
Twelve degrees, thirty arcminutes.
Questions people ask
1Why does ′ show as a box on some devices?
Because that device's fonts have no glyph for it. The character is still correct and still copies correctly — the box is a missing glyph, not a broken character.
How to type ′
Windows (Word)
Alt+XType 2032, then Alt+X to get ′.
Windows
Win+Rrun charmap for the full table, or use the emoji picker's Ω symbols tab (Win + .).
macOS
Control+Command+SpaceOpen the character viewer and search “prime”.
Linux
Ctrl+Shift+UType 2032, then Enter or Space.
HTML
′CSS
\2032How to type the prime symbol
Copy it from the palette.
Codes and encoding1 code points
HTML decimal
′
HTML hex
′
CSS content
content: "\2032";
Each escape is closed by the next backslash; a trailing space is needed before a literal hex digit.
URL encoded
%E2%80%B2
1
On screen
1
Code points
1
JS .length
3
UTF-8 bytes
A visible symbol can contain several code points. JS .length counts UTF-16 units; UTF-8 counts bytes.