Pixels and Accessibility

As someone with poor vision, I don&#x27;t want &quot;make everything bigger&quot;, and I don&#x27;t want &quot;make all the text bigger&quot;, I want &quot;make the small text bigger&quot;.<p>(Or, ideally, &quot;make small text and fiddly diagrams bigger, but leave most images alone&quot;, but let&#x27;s walk before we try to run.)<p>So maybe &quot;rems for body text, px for headings&quot; is the way to go.

&gt; <i>1px is equal to a single dot in a computer monitor or phone screen.</i><p>Far from always!<p>“For screen displays, it traditionally represents one device pixel (dot). However, for <i>printers and high-resolution screens</i>, one CSS pixel implies multiple device pixels. 1px = 1&#x2F;96th of 1in.”<p>— <a href="https:&#x2F;&#x2F;developer.mozilla.org&#x2F;en-US&#x2F;docs&#x2F;Web&#x2F;CSS&#x2F;length" rel="nofollow">https:&#x2F;&#x2F;developer.mozilla.org&#x2F;en-US&#x2F;docs&#x2F;Web&#x2F;CSS&#x2F;length</a>

This is one of the long form frontend blogs that I greatly enjoy, and learn sometime new every time. So, I am excited anytime a new one comes out. I hope with Josh releasing his own course[1], that the blog continues to provide excellent resources for &quot;free&quot;.<p>[1](<a href="https:&#x2F;&#x2F;css-for-js.dev&#x2F;" rel="nofollow">https:&#x2F;&#x2F;css-for-js.dev&#x2F;</a>)

It&#x27;d be more accurate and illuminating to say that a px is an angle.<p><i>The reference pixel is the visual angle of one pixel on a device with a pixel density of 96dpi and a distance from the reader of an arm’s length. For a nominal arm’s length of 28 inches, the visual angle is therefore about 0.0213 degrees. For reading at arm’s length, 1px thus corresponds to about 0.26 mm (1&#x2F;96 inch).</i> - <a href="https:&#x2F;&#x2F;www.w3.org&#x2F;TR&#x2F;css-values-4&#x2F;#absolute-lengths" rel="nofollow">https:&#x2F;&#x2F;www.w3.org&#x2F;TR&#x2F;css-values-4&#x2F;#absolute-lengths</a><p>This explains why 1px is small on phones and large on televisions; the physical size varies by expected reader distance. The angle tries to stay constant, though in practice it gets rounded to the nearest multiple of the physical pixel size.

It&#x27;s quite ironic how the font settings page for Chrome doesn&#x27;t do well with different font sizes itself. They got the sidebar backwards and appeared to have used px for the font-size but em for the padding.

&gt; <i>In theory, 1px is equal to a single dot in a computer monitor or phone screen.</i><p>Even in theory, this has never been true AFAIK. Pixels (px) are relative to the properties of the viewing device, the user&#x27;s OS and browser settings, etc. The author appears to be confusing &quot;physical pixel&quot; with &quot;logical pixel&quot;.