Horizonal frequency, (like 15 for PAl and 30 for VGA) is measured in kHz
Vertical frequency (like 60 for a flickery picture and 100 for a non flickery picture) is measured in Hz.
These pages explain it in some detail:
http://en.wikipedia.org/wiki/Refresh_rate
http://en.wikipedia.org/wiki/Horizontal_scan_rate
Although you might want to read other pages as well for more information, due to the strange use of the word 'shuzam' in the Refresh Rate article.
And to verify that horizontal refresh rate is measured in kHz, my monitor's OSD states the horizonal rates it can do in kHz and the vertical rates it can do in Hz.