The CDs arrived in good order here in The Netherlands, thanks! For those who want to compare the formulas with the outcome of the spreadsheet, Stephen adds 10% to the wanted final length, in the spreadsheet i work with percentage reduction from the unfurled threads. Example, for a 72" leader Stephen uses 72 + 7.2(=10%)= 79.2" for the unfurled length.
I use 72 + 8(10% from 80) = 80" for the unfurled length.
Just something to take into account, no big deal.

Karel