'Hertz' is a unit of frequency meaning 'cycles per second' - which is exactly as the documentation describes it
It gets translated internaly into milli gap, that is if I say 60Hrtz it doesnt fire at 60Hrtz, it fires at 1000/60 milli (16.66666666), which is different. (And dont go saying oh but, cos they are not the same)
http://www.blitzbasic.com/Community/posts.php?topic=59885#667937