Couple snag affordable unit after two-year quest

[EnSabahNur]

If you just look at the headlines, it would seem "affordable" for this couple. But note that the cost of the flat (at $340,000) is nearly 8x of their household annual income of $42,000. I am not sure how they can measure affordability this way....

What is the rule of the thumb for a normal ratio?

This article seems unconvincing