The initial formula is in C3
$A$3 is the cell that you enter the time you want to convert, this is "anchored" to both row and column.
MATCH($A2,$C$1:$N$1,0), this returns the position in the range $C$1:$N$1 of the time zone that you choose in B2.
OFFSET($B$2,0,MATCH($A2,$C$1:$N$1,0)) returns the time difference relative to GMT, by using B2 as a reference we can simply use the value returned by the match formula.
The rest is just arithmetic to calculate the relative differences between your chosen zone and the others.
I have added a break down of the formula to the amended workbook attached.
I have also added this formula to row 5
It is an easier and non-volatile way to do the same thing, I just hammered down the first thing that came to my head in my first post.
Hope this helps
Bookmarks