Zoom level v pixel/em experiment

Measurement: pixels to show 10em.

1. Vary your browser's text-zoom level.
2. Refresh.
3. Record the zoom level and the above measurement.

The tool is simple -- the red bar is 10 em wide and varies with zoom level. There is a javascript routine that measures the actual width of the bar in pixels. As such, you can measure how much the zoom level effects em -- and from that you can determine how much font-size is decreased/increased per zoom level per browser.