Can a Credit Card Really Be Used to Calibrate an On-Screen Ruler?

[NightHollow]

I recently discovered that a standard bank card can act as a physical reference when you don't know your display's exact dimensions. Has anyone tried this method, and how close were the resulting measurements to a real ruler? The site uses the standard 85.6 mm card width as one of its calibration methods.

[jaidenllmerritt]

I know this thread is a bit old, but I wanted to chime in. The credit card method is pretty handy, but its accuracy depends on how carefully you line up the edges on your screen. Even a tiny finger slip can throw off the pixel scale. Have you tested the on-screen ruler against a physical ruler on the same display to see how close they actually match?

[rzaasiriy985]

The credit card method is decent for rough checks, but it depends on how carefully you align the edges. I have found that calibrating with the exact screen diagonal gives more consistent results, since card widths can vary slightly with embossing or wear. For a quick reference, I often use ruler on phone and compare it against a physical ruler; it matches well enough for everyday tasks.