Dont understand

Hi all I was hopeing that you could tell me what this file is doing is simple math terms.
http://www.freewebs.com/thecrankyhermit/wsRubrick.zip

I'm trying to build a php based version of this file for a site. and I'm not familar with excel funtions. like
=IF(ISERROR(VLOOKUP(E210,Lookup!$A$17:$C$21, 3, FALSE)), 80, VLOOKUP(E210,Lookup!$A$17:$C$21, 3, FALSE))
I know it's kinda asking alot but i hope some excel guru out there can help.

=IF(ISERROR(VLOOKUP(E210,Lookup!$A$17:$C$21, 3, FALSE)), 80, VLOOKUP(E210,Lookup!$A$17:$C$21, 3, FALSE))


Ok its the combiation of 3 functions

Firstly the vlookup function is vlookup(value,range,column,match)
in your formula it is looking up the value in e210 trying to match it exactly in the cells a17:a21 in the llokup worksheet and if it finds a match return the value in column3

So if the match is in a19 it will return the value in c19. the false means this match has to be exact, falilure to make a match will return #n/a an error, its saying it is not applicable

iserror returns true if there is an error (#n/a is classed as an error) or false if there is no error

an if statement is if(true,do this,else do that)


so the whole formula, if you have still got the will to live returns 90 if no match is found otherwise performs the lookup and returns the appropriate value

Regards

Dav