In several datasheets for electronic components, I have seen a ∝ symbol used as a prefix for a time unit, usually seconds, writing as ∝s. As far as I know ∝ is not a valid SI prefix, so what does it mean? What unit is ∝s?

Comparing different datasheets, I assume it should be rather equivalent to micro prefix, but I'm really not sure.

You can see this use for example in the BT136 datasheet describing "Gate controlled turn-on time" and defining unit as ∝s.

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  • 3
    \$\begingroup\$ Shows up perfectly fine here as µs (Safari, macOS), even with the embedded viewer on that site, or by downloading the PDF and opening it in Preview. \$\endgroup\$
    – jcaron
    May 25 at 17:30
  • 2
    \$\begingroup\$ You just have a problem with your PDF reader, and this is not about electronics. \$\endgroup\$ May 25 at 21:37
  • \$\begingroup\$ The PDF also shows fine with μs on Firefox/Linux. Sounds like a Microsoft fail (though I doubt it's an issue in up-to-date versions of Windows and browsers). Really, character encodings should be a non-issue nowadays... utf8everywhere.org \$\endgroup\$ 2 days ago
  • 2
    \$\begingroup\$ Irrespective of the root cause, I think it's useful that this has been brought to the community's attention. \$\endgroup\$ yesterday

2 Answers 2


In the common ISO 8859-1 encoding, µ is encoded as 0xB5.

In the Windows Symbol typeface, ∝ is encoded as 0xB5.

The Symbol font has been commonly used for Greek letters; µ is the only Greek letter that is available elsewhere. This appears to be a common mistake.

  • 7
    \$\begingroup\$ That's a common issue with Ω (Greek capital omega) for Ohm, with so many documents and datasheets showing a W instead - generating confusion, sometimes. Then it's far better IMHO using the lowercase u, even though improperly used \$\endgroup\$
    – LuC
    May 24 at 10:12
  • 8
    \$\begingroup\$ I downloaded the datasheet as a PDF (rather than viewing in the Alldatasheet.com viewer) and the symbol renders correctly. (Most likely the font is embedded in the PDF.) \$\endgroup\$
    – Theodore
    May 24 at 20:56
  • \$\begingroup\$ The issue (∝ shows where µ should) occurs independently of browser and OS: it's specific to using the obsolete PDF viewer (pdfjsview) at pdf1.alldatasheet.com/pdfjsview/web/viewer.html (which is used or not depending on browser). The issue occurs neither in the pure html version, nor if the pdf itself is viewed, or downloaded and viewed. \$\endgroup\$
    – fgrieu
    2 days ago

It is most likely an encoding error in the PDF file. It is simply the wrong symbol.

Here's a section of the BT136 datasheet showing the dynamic characteristics:

enter image description here

It shows ∝s for several things, among them \$dV_{com}/dt\$.

Figure 12 also refers to \$dV_{com}/dt\$, but it uses units of microseconds (us.)

enter image description here

Figure 12 uses the common (also incorrect) convention of using a lower case "u" for micro rather than the correct µ symbol. The dynamic characteristics table probably had the correct symbol in whatever program was used to write the datasheet, but it got mangled in the conversion to PDF.

  • 4
    \$\begingroup\$ The PDF is fine; your viewer is what's broken. \$\endgroup\$
    – Ben Voigt
    May 25 at 17:03
  • \$\begingroup\$ @Ben-Voight Did you notice that the original post links to an HTML document? \$\endgroup\$
    – david
    2 days ago
  • \$\begingroup\$ @david, did you notice that the HTML document has embedded PDF content? \$\endgroup\$ 2 days ago

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