some really useful things they didn't tell you in the tutorial on calculating dates...

how to add 1 day or a week to a date

if you have a date in A1, and you want to add 1 day in A2, in A2, put in =A1+1 — you will find that the serial numbers for days are simply integers incremented by 1. for a week, 7, for 3 weeks, 21. but don't try doing the entire date calculation yourself, it won't work, excel does it funny, and besides, gregorian calendars are kind of complicated anyway. I would stay away from calculating months since there are 30/31/28/29 days in a month in each case.

how to add 1 hour to a date+time

if you have a date+time in A1, and you want to add 1 hour in A2, in A2, put in =A1+1/24 — you must multiply your integer hour by 1/24 and add it to the original number (A2=A1+hour/24).

how to add 1 minute to a date+time

if you have a date+time in A1, and you want to add 1 minute in A2, in A2, put in =A1+1/1440 — you must multiply your integer minute by 1/1440 (or 1/(24*60) and add it to the original number (A2=A1+minute/1440).

how to add 1 second to a date+time

if you have a date+time in A1, and you want to add 1 second in A2, in A2, put in =A1+1/86400 — you must multiply your integer minute by 1/86400 (or 1/(24*60*60) and add it to the original number (A2=A1+minute/86400).

how to add 1/10 second to a date+time

if you have a date+time in A1, and you want to add 1/10 second in A2, in A2, put in =A1+1/864000 — you must multiply your integer minute by 1/864000 (or 1/(24*60*60*10) and add it to the original number (A2=A1+minute/864000).

full time calculation

timecode=integerDay + integerHour/24 + integerMinute/(24*60) + integerSecond/(24*60*60) + integerTenthSecond/(24*60*60*10)