I stared at this pen for a long time trying to decipher the brand name – but I had no problem reading the words KING SIZE.
Turn it the right way around and it's the familiar Sharpies brand. Have I just developed a new legibility test?
In my early career at the Open University I used multiple photocopying passes to show how some typefaces degrade more quickly than others - try it with Arial vs Bodoni and you'll see what I mean, although it worked better before photocopiers went digital.
You can also compare how easy it is to read typefaces through multiple layers of tracing paper. My business partner David Lewis used the term Strudel Test for this - following his mother's measure of when strudel pastry was thin enough (can you read a newspaper through it?).