This character is a Other Symbol and is commonly used, that is, in no specific script.
The glyph is a square composition of the glyphs Latin Small Letter N, Latin Small Letter M. Its East Asian Width is wide. In bidirectional text it is written from left to right. When changing direction it is not mirrored. U+339A offers a line break opportunity at its position, except in some numeric contexts.
The Wikipedia has the following information about this codepoint:
The nanometre (international spelling as used by the International Bureau of Weights and Measures; SI symbol: nm), or nanometer (American spelling), is a unit of length in the International System of Units (SI), equal to one billionth (short scale) of a meter (0.000000001 m) and to 1000 picometres. One nanometre can be expressed in scientific notation as 1 × 10-9 m and as 1/1000000000 m.
Representations
System
Representation (click value to copy)
Nº
13210
UTF-8
E3 8E 9A
UTF-16
33 9A
UTF-32
00 00 33 9A
URL-Quoted
%E3%8E%9A
HTML hex reference
㎚
Wrong windows-1252 Mojibake
㎚
Encoding: CP949 (hex bytes)
A7 AC
Encoding: EUC_KR (hex bytes)
A7 AC
Encoding: GB18030 (hex bytes)
81 39 E5 36
Encoding: ISO2022_JP_2 (hex bytes)
1B 24 28 43 27 2C 1B 28 42
Encoding: ISO2022_KR (hex bytes)
1B 24 29 43 0E 27 2C 0F
Encoding: JOHAB (hex bytes)
DC 3C
Adobe Glyph List
nmsquare
RFC 5137
\u'339A'
Bash and Zsh inside echo -e
\u339A
C and C++
\u339A
C#
\u339A
CSS
\00339A
Excel
=UNICHAR(13210)
Go
\u339A
JavaScript
\u339A
Modern JavaScript since ES6
\u{339a}
JSON
\u339A
Java
\u339A
Lua
\u{339A}
Matlab
char(13210)
Perl
"\x{339A}"
PHP
\u{339a}
PostgreSQL
U&'\339A'
PowerShell
`u{339A}
Python
\u339A
Ruby
\u{339a}
Rust
\u{339a}
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