Page not fitted to the mobile width
On a phone it shows the desktop version shrunk down: tiny text, and dragging sideways to read one line.
When we count it as met
When we measure the same pages again, all of them declare a viewport tag.
How to check it yourself
Confirm it by opening the page code: the meta viewport tag appears in its head.
Measure it on your site
UXMachine measures it in a real browser, on desktop and mobile, together with the other checks.