I think you are looking for the 8870 System for computing a birth date from death information. Example: ( d. May 6, 1889, age 71 yrs, 7 mo, 9 days) Yr. Mo. Day Write Date - 18890506 Subtract Death Info 710709 18179797 Subtract 8870 18170927 = Yr.1817, Mo. 09, Day 27 Most of the time this works fairly well, however there are times the final number will have to be worked on further to get it to an actual yr, mo, and day that makes sense. You'll see what I mean when it actually comes out with an odd calculation. Joan