The other day I realized that I enter my haircut appointments into Google Calendar, so I can search for “haircut OR (the place I get my hair cut)” and see when I’ve gotten my hair cut:
Then I was reading Google Apps Hacks and Hack 25 caught my eye: “Show the difference between two dates”. A formula like “=INT(A2-A1)” will automatically compute how many days passed between the date listed in cell A1 and the date listed in cell A2.
If you copy and paste a date from Google Calendar’s search results into a cell, it will automatically format a nice string like “May 2, 2007″ to “5/2/2007″. So it was easy to copy/paste when I got haircuts into a Google Spreadsheet. Then I used the date formula to compute the number of days between haircuts. As Philipp Lenssen points out in his book, once you’ve entered the date difference formula “=INT(A2-A1)” in one cell, you can click the cell to highlight it and then use the handle in the lower right of the cell to copy the formula. Just like that, you can see how long you waited between each haircut:
Then it’s just 2-3 mouse clicks to add a graph of the time between haircuts. And if you use the “=AVERAGE(B3:B10)” formula, you can see that on average I wait 45.75 days between haircuts, or about 6-7 weeks.
This tip does have some practical value. When the haircut place asks “Do you want to make your next appointment?” you’ll know how far ahead to schedule your next haircut so that you don’t get too shaggy.