Very crafty! This does exactly what I need, but I'm having a problem with
the calculations taking far too long and weighing down the spreadsheet every
time they decide to recalculate (I'm not always certain why it recalculates).
I've got about 30,000 rows of data. Can you think of any way to streamline
this without just removing the formula and preserving the values?
Thanks for your help!

"Herbert Seidenberg" wrote:

Add helper column to source data:
http://www.savefile.com/files/1681330