# ψ used as diameter, which unit is this?

I am designing a PCB footprint for this part: https://www.meanwell.com/productPdf.aspx?i=685

On page 4, the pins diameters are indicated as: diameter:1ψ and diameter:2ψ

Also, on the quotes, they are using 2-1ψ and 2-2ψ

I searched the web for answers but could not find anything useful..

What is ψ? Why is it used instead of millimeters? How can I convert this to metric? How large are the diameters of these pins?

• I guess they simply mistook the '⌀' for a 'ψ' to denote 'diameter'. The unit should be millimeter still. "2-1" should be read as 2 times 1mm (as there are two pins). Commented Jan 2, 2021 at 11:18
• The sign appeares in many meanwell documents... google.com/search?q=meanwell+%CF%88 Commented Jan 2, 2021 at 14:31
• They probably intended to use an upper case phi. Which is still wrong, a diameter symbol has the slash at an angle. Commented Jan 2, 2021 at 15:21

That is not a letter "psi". It is diameter sign. 4 holes with diameter 3.5 millimeter.

• Nope, that is an actual Unicode character ψ in the document. Commented Jan 2, 2021 at 13:31
• Yes, you right. So may be file creator mistake. Commented Jan 2, 2021 at 13:34
• a quick google search shows many meanwell PDFs with the sign making it not likely a mistake... google.com/search?q=meanwell+%CF%88 Commented Jan 2, 2021 at 14:29
• How did you reach the 3.5mm number? Also considering the 4 pins have two different sizes... Commented Jan 2, 2021 at 14:34
• 3.50mm 4 holes. Page 4 in the link, OP provided. I did not reach but read that. Why Meanwell using that sign is only Meanwtell documents writer knows. I do not insist, only guess. Commented Jan 2, 2021 at 16:04

The same character shows up in their datasheets to mean phase.

If I copy the character out of the datasheet and paste it into a blank PDF, there is a warning of font substitution and this Arial character is pasted:

Maybe a muck-up similar to the frequently-seen Ω/W substitution in pdf datasheets.

The original uses a number of traditional/simplified Chinese fonts, apparently from the Mac world.

So the meaning should not be uncertain, despite the similarity to the wave equation.