Hi all This is probably a real newbie error, but PHP's is_nan function is not playing for me. I've got this as a test: <? $tester = "hello"; if (is_nan($tester)) { echo "this works"; exit; } else { echo "don't work"; exit; } ?> And I get back: Warning: is_nan() expects parameter 1 to be double, string given in (address of the page) Why?! Regards Francis