I also did my own reverse engineering of the NOAA excelsheet. And to to basically same formula's except for one. Richard Droste's last line reads: X = (720-4lng-V+UTCoff60)60; However the calculation in column X, line 2 of the NOAA excel sheet reads: "=(720-4$B$3-V2+$B$4*60)/1440, where $B$3 is "lng" and $B$4 is UTCoff in Richards definition. Hence the difference is NOAA is dividing by "1440" at the end and Richard is taking "60". i assume he's accounting for the missing factor "24" (1440/60) in his time conversions later on.