₀ Subscript Zero
Subscript zero (₀) is a real character for the index 0 — x₀, H₀ — that survives copy-paste into plain text, unlike a word processor's subscript formatting.
Also known as: subscript 0, subscript zero, small 0 below, x naught symbol.
Codes
| Symbol | ₀ | |
| Full run 0-9 | ₀₁₂₃₄₅₆₇₈₉ | |
| Unicode | U+2080 | |
| HTML entity (decimal) | ₀ | |
| HTML entity (hex) | ₀ | |
| CSS | \2080 | |
| LaTeX | x_0 | |
| Windows Alt code | Alt + 8320 |
How to type ₀ (Subscript Zero)
Alt + 8320 works in apps that accept decimal-Unicode Alt input (Word among them). There is no short Alt + 0nnn code — the subscript digits are outside the legacy code pages. Elsewhere press Win + . (period) and search “subscript”, or copy ₀ above.
No default keystroke. Open Character Viewer (Control + Cmd + Space) and search “subscript zero”, or copy ₀ above.
Type 2080, then press Alt + X to get the character ₀. This is different from Ctrl + = , which applies subscript *formatting* to a normal 0 — see Usage below for why the difference matters.
Insert → Special characters, then search “subscript zero”. (Ctrl + , applies subscript formatting instead, which is not the same thing.)
In math mode write x_0; braces are needed only for more than one character, as in x_{10}. Do not paste ₀ into LaTeX source — use the underscore.
Usage
- x₀ is the initial value or the starting point of a sequence, and t₀ the initial time.
- In statistics H₀ is the null hypothesis — the claim you test against, read “H-naught” or “H-zero”.
- Which one to use — this is the whole point of the character: ₀ (U+2080) is a *character*. A word processor's subscript button applies *formatting* to an ordinary 0. Formatting looks identical on screen, but it is lost the moment the text is pasted into a plain-text field — a CSV cell, a code comment, a chat box, an email subject line. If your subscript has to survive travel, use the character.
- The trade-off: because ₀ is one character, no font-size rule or superscript toggle applies to it, and some search boxes will not match it against a plain 0.