Recently I noticed that my square root symbol is looking really ugly:

That gap. We can see Pennywise eating Georgie throught it.

The square root per se is not correctly connected to the overbar. The picture above is with a small zoom factor. When I zoom in we can see that the overbar is slightly below the top of the square root. Both look pretty bad.

That miss

At first I thought that it was due to the math font I'm using, so I tried the rawest possible example:

  \[A_m = \sqrt{2\mathcal{S}(f)\Delta f}\]

And there we have it:

Another gap

Also browsing through the Similar Questions while writing this one, I saw that this happens quite often (e.g.:This answer, and this one).

What causes this and how to solve it?

  • 3
    It seems more like a viewer issue; try looking at maximum magnification. I see nothing like that. – egreg Nov 12 '17 at 13:30
  • I also thought so, but I used three different viewers (Okular, Evince and Acrobat), and all of them resulted the same. The maximum magnification is in the second picture. I didn't try printing it though... – Phelype Oleinik Nov 12 '17 at 13:35
  • 3
    @PhelypeOleinik basically the two lines are lined up in the pdf but the font hinting and rules are separately aligned to the pixel grid of your physical device and it depends on the exact arithmetic and heuristics used by your pdf viewer, so basically no you can't stop a jagged join appearing at all resolutions in all pdf viewers – David Carlisle Nov 12 '17 at 15:21
  • 1
    I can confirm that mwe.pdf looks fine even at highest resolution on my Mac OS both with Adobe Acrobat and with Skim. (and also inside the Viewer in Firefox when going to the Dropbox link) – user4686 Nov 12 '17 at 15:27
  • 1
    @jfbu Indeed, the viewer in Firefox renders the pdf perfectly. Thanks! – Phelype Oleinik Nov 12 '17 at 15:40