Zend certified PHP/Magento developer

emacs monospace font not aliging when I increase text size

I noticed that although the default emacs (GUI) font claims to be monospaced the columns don’t match up (e.g. the 30th column on one row is not vertically aligned with the 30th column of another). It appears to work properly when I increase it past that point it breaks. Anyone know what the problem might be?