Back porch, front porch?

When first running Advance Mame, I'm trying to customize the video profile
for my NEC accusync 900 monitor.  I am able to enter the vertical and
horizontal refresh rates, but what are vertical & horizontal front, back,
etc. porches?  I need to enter 12 numbers, but have no idea what to enter.
I understand that the horizontal and vertical actives are the values of my
screen resolution, but don't know what the rest are (or mean).  I looked
through my manual, and the only specs of the monitor are refresh rates &
resolutions.  Link to manual is here.
<http://www.necdisplay.com/corpus/D/G/AccuSync_CRT_Series_Brochure_0405.pdf>
It then asks for "pixel clock", horz clock and vert clock.  I know the last
2, but not pixel clock.  If I enter the example porches, then put in my own
horz and vert clock, and enter 5-10 for the pixel clock, it then goes to the
centering screen, but its all blurry and illegible.  Does anyone have any
ideas?