It would be remiss of me not to mention that you really ought to re-consider making a spreadsheet an integral part of your design, not the least due to the historically high rates of error that have been measured in spreadsheets - 1 to 5%: https://arxiv.org/ftp/arxiv/papers/1602/1602.02601.pdf . It seems incongruous to worry about the sixth decimal place in numbers with many digits before the decimal point but ignoring error rates that dwarf this imprecision.
By way of comparison, in most code-bases where people measure errors, an error rate of 10 bad lines per 1000 lines of code would be considered unacceptably high. ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm
