A rem is not a rem?

Question

I've got strange result on an Android device while trying to use rem unit for adaptive HTML page. When opening this fiddle on any device, I expect to see "640" in the alert message. It works well on all my devices except of a tablet pc where it shows 832. Why?

html:

<div id="div"></div>

css:

html {
  font-size: 640px;
}
#div {
  width: 1rem;
}

js:

$(window).load(alert($('#div').width()))

Device info:

• Prestigio MultiPad PMP5580C
• Android 4.1.1
• Built-in Browser app
• Screen resolution: 1024x768

Answer 1

The problem was caused by the "Text scaling" browser feature. It was set to 130%.