How do you set the watch for est...

In the time keeping mode hold down the bottom button until a letter starts to flash in the square. Once it's flashing press and release the top button as many times as needed until you get an "E" in the square. Once it has an "E" in the square press the bottom button a total of 10 times to exit the setting mode.

If you need the manual here is a link:

http://ftp.casio.co.jp/pub/world_manual/wat/en/qw4303.pdf