I'm glad to report that a much improved version of the spreadsheet is now available. It is flexible enough to deal with 21 and 31-step tablets and has an improved interface, allowing for some user intervention at every stage to provide more robust results. Detailed instructions are not quite done yet but should be available by Sunday.
You'll find it again at:
As far as I can tell, it should be compatible with OpenOffice without recoding, but I have no way to check that. Therefore, I hope you will report back with any issues you may have.
PS: It would help me to improve this spreadsheet if people could supply 21 and 31-step sample data to firstname.lastname@example.org.
Thanks in advance.