formula
 

formula:
i am pretty sure some friends will appropriately add lines here, but let there was a similar discussion a couple of months ago in this forum and i remember riz offered a spreadsheet even.
i thought you might want to go through previous threads as you wait for detailed responses.
good luck
ed, it says that you are a visitor. now to access the thread i have mentioned, do the following
1) click on keyword search tab
2) in the keyword field type: helical
3) select structural forum radio button
and begin the search.
good luck