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Article originally by Liberty Miller , last edited by Liberty Miller on 2007-Oct-28 2008-February (sp.) 
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A way of writing "approximately equal to" ("almost equal to" \ "equals approximately" \ "approximately equals") in standard internet-based text * or plain text applications:

=~

  This text can be read aloud as "equals approximately" or "is approximately equal to".

Examples:

  • 1 MB (MegaByte) = 1,024 KB (KiloBytes) = 1,048,576 Bytes = 8,388,608 bits =~ one million Bytes
    "One megabyte ... is equal to eight million, three hundred eighty-eight thousand, six hundred and eight bits, (which) is approximately equal to one million bytes."
    "One megabyte ... equals eight million, three hundred eighty-eight thousand, six hundred and eight bits, (which) equals approximately one million bytes."
  • 1 GB =~ 1 Billion Bytes (1 GB = 1,073,741,824 Bytes)
    "One gigabyte is approximately equal to one billion bytes... ."
    "One gigabyte equals approximately one billion bytes... ."

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* email, comment forms, forums, message boards, et cetera

Rationale

Related quote from the WWW:

"7^2 = 50 (that should be an "is approximately equal to" symbol, but I'm too lazy to figure out how to get one of them)..."

The preferred way of symbolizing "approximately equal to" is to use the ≈ symbol, the ~ symbol, or (in some cases) the ≅ symbol (see note 2).

  However:
• ≅ and ≈ are symbols that are not easy for people to enter in email, forums, etc. (no standardized keyboard entry method).
• ≅ and ≈ are symbols that are not universally rendered correctly in web browsers (in fact, you may be seeing boxes instead of symbols right now) and are not commonly parsed correctly in web tools like commenting and forums.
• the ~ symbol is too often to indicate some other meaning (e.g. 'NOT'), or decoratively.
( Note: In HTML 4 "~" is defined as "varies with" or "similar to".)

"=~" is an easy to use and easy to remember alternative.

Why not ~= ?

"~=" is a logical possible expansion of , which many people interpret as "approximatley equals" (rather than as the useage of 'congrunet' in geometry).
Furthermore, "~=" could be read as "approximately equals". However, in some programming languages, '~' is symbolic of NOT (Bitwise), and '~=' is therefore somtimes used as a variation of '!=', which means NOT EQUAL TO. Because of this potential source of confusion, "=~" is proposed instead.

 

Preferred symbols

If text can be entered as HTML, you can also use the following notations:

  • ≈ ( ≈ ) [approximately-equal-to symbol; "asymptotic to, U+2248"]
  • ≈ ( ≈ ) [Decimal NCR notation]
  • =~ ( =~ )
Note 1: "asymptotic to, U+2248" means, more precisely, "almost equal to"; often, if the approximation is broader\less precise, ~ is preferred.
Note 2: ≅ (≅ 'U+2245') is defined in HTML 4 as "cong" : "is congruent to" -- having exactly or very nearly the same size and shape, having correspondence; having the same characteristics

 

Related links:
w3.org's HTML SYMBOL Characters and Glyphs (www.w3.org /Math)
HTML Character Codes
Numeric Character References (NCRs) [Representing Characters in HTML]
Algebra -- Math Symbols (gomath.com)



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